diff --git a/lib/inboundDomains.js b/lib/inboundDomains.js
index 9549c0f..3f52303 100644
--- a/lib/inboundDomains.js
+++ b/lib/inboundDomains.js
@@ -1,6 +1,5 @@
 'use strict';
 
-const withCallback = require('./Promise');
 const api = 'inbound-domains';
 
 module.exports = function(client) {
@@ -15,7 +14,7 @@ module.exports = function(client) {
       const options = {
         uri: api
       };
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
     /**
      * Get an inbound domain by its domain name
@@ -26,13 +25,13 @@ module.exports = function(client) {
      */
     get: function(domain, callback) {
       if (!domain || typeof domain !== 'string') {
-        return withCallback(Promise.reject(new Error('domain is required')), callback);
+        return client.reject(new Error('domain is required'), callback);
       }
 
       const options = {
         uri: `${api}/${domain}`
       };
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
     /**
      * Create a new inbound domain
@@ -43,14 +42,14 @@ module.exports = function(client) {
      */
     create: function(createOpts, callback) {
       if (!createOpts || typeof createOpts !== 'object') {
-        return withCallback(Promise.reject(new Error('create options are required')), callback);
+        return client.reject(new Error('create options are required'), callback);
       }
 
       const options = {
         uri: api
         , json: createOpts
       };
-      return withCallback(client.post(options, callback), callback);
+      return client.post(options, callback);
     },
     /**
      * Delete an existing inbound domain
@@ -61,13 +60,13 @@ module.exports = function(client) {
      */
     delete: function(domain, callback) {
       if (!domain || typeof domain !== 'string') {
-        return withCallback(Promise.reject(new Error('domain is required')), callback);
+        return client.reject(new Error('domain is required'), callback);
       }
 
       const options = {
         uri: `${api}/${domain}`
       };
-      return withCallback(client.delete(options), callback);
+      return client.delete(options, callback);
     }
   };
 };
diff --git a/lib/messageEvents.js b/lib/messageEvents.js
index 98c1e90..6d468d0 100644
--- a/lib/messageEvents.js
+++ b/lib/messageEvents.js
@@ -1,6 +1,5 @@
 'use strict';
 
-const withCallback = require('./Promise');
 const api = 'message-events';
 
 /*
@@ -29,7 +28,7 @@ module.exports = function(client) {
           options.qs[paramname] = parameters[paramname];
         }
       });
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     }
   };
 };
diff --git a/lib/recipientLists.js b/lib/recipientLists.js
index 5c5eeee..a4f7364 100644
--- a/lib/recipientLists.js
+++ b/lib/recipientLists.js
@@ -1,6 +1,5 @@
 'use strict';
 
-const withCallback = require('./Promise');
 const api = 'recipient-lists';
 
 module.exports = function(client) {
@@ -16,7 +15,7 @@ module.exports = function(client) {
       const reqOpts = {
         uri: api
       };
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     },
 
     /**
@@ -38,7 +37,7 @@ module.exports = function(client) {
       }
 
       if (!id) {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       const reqOpts = {
@@ -46,7 +45,7 @@ module.exports = function(client) {
         qs: options
       };
 
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     },
 
 
@@ -61,7 +60,7 @@ module.exports = function(client) {
      */
     create: function(recipientList, callback) {
       if (!recipientList || typeof recipientList !== 'object' || !recipientList.recipients) {
-        return withCallback(Promise.reject(new Error('recipient list is required')), callback);
+        return client.reject(new Error('recipient list is required'), callback);
       }
 
       const reqOpts = {
@@ -72,7 +71,7 @@ module.exports = function(client) {
         }
       };
 
-      return withCallback(client.post(reqOpts), callback);
+      return client.post(reqOpts, callback);
     },
 
     /**
@@ -88,11 +87,11 @@ module.exports = function(client) {
      */
     update: function(id, recipientList, callback) {
       if (!id) {
-        return withCallback(Promise.reject(new Error('recipient list id is required')), callback);
+        return client.reject(new Error('recipient list id is required'), callback);
       }
 
       if (!recipientList || typeof recipientList === 'function') {
-        return withCallback(Promise.reject(new Error('recipient list is required')), callback);
+        return client.reject(new Error('recipient list is required'), callback);
       }
 
       const reqOpts = {
@@ -103,7 +102,7 @@ module.exports = function(client) {
         }
       };
 
-      return withCallback(client.put(reqOpts), callback);
+      return client.put(reqOpts, callback);
     },
 
     /**
@@ -117,14 +116,14 @@ module.exports = function(client) {
      */
     delete: function(id, callback) {
       if (!id || typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       const reqOpts = {
         uri: `${api}/${id}`
       };
 
-      return withCallback(client.delete(reqOpts), callback);
+      return client.delete(reqOpts, callback);
     }
   };
 
diff --git a/lib/relayWebhooks.js b/lib/relayWebhooks.js
index a368763..9126aea 100644
--- a/lib/relayWebhooks.js
+++ b/lib/relayWebhooks.js
@@ -1,6 +1,5 @@
 'use strict';
 
-const withCallback = require('./Promise');
 const api = 'relay-webhooks';
 
 module.exports = function(client) {
@@ -15,7 +14,7 @@ module.exports = function(client) {
       const reqOpts = {
         uri: api
       };
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     },
     /**
      * Get details about a specified relay webhook by its id
@@ -26,14 +25,14 @@ module.exports = function(client) {
      */
     get: function(id, callback) {
       if (!id || typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       const options = {
         uri: `${api}/${id}`
       };
 
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
     /**
      * Create a new relay webhook
@@ -44,7 +43,7 @@ module.exports = function(client) {
      */
     create: function(webhook, callback) {
       if (!webhook || typeof webhook !== 'object') {
-        return withCallback(Promise.reject(new Error('webhook object is required')), callback);
+        return client.reject(new Error('webhook object is required'), callback);
       }
 
       const reqOpts = {
@@ -52,7 +51,7 @@ module.exports = function(client) {
         , json: webhook
       };
 
-      return withCallback(client.post(reqOpts), callback);
+      return client.post(reqOpts, callback);
     },
     /**
      * Update an existing relay webhook
@@ -64,11 +63,11 @@ module.exports = function(client) {
      */
     update: function(id, webhook, callback) {
       if (!id || typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       if (!webhook || typeof webhook !== 'object') {
-        return withCallback(Promise.reject(new Error('webhook object is required')), callback);
+        return client.reject(new Error('webhook object is required'), callback);
       }
 
       const reqOpts = {
@@ -76,7 +75,7 @@ module.exports = function(client) {
         , json: webhook
       };
 
-      return withCallback(client.put(reqOpts), callback);
+      return client.put(reqOpts, callback);
     },
     /**
      * Delete an existing relay webhook
@@ -87,14 +86,14 @@ module.exports = function(client) {
      */
     delete: function(id, callback) {
       if (!id || typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       const options = {
         uri: `${api}/${id}`
       };
 
-      return withCallback(client.delete(options, callback), callback);
+      return client.delete(options, callback);
     }
   };
 };
diff --git a/lib/sendingDomains.js b/lib/sendingDomains.js
index 43698e9..b28559d 100644
--- a/lib/sendingDomains.js
+++ b/lib/sendingDomains.js
@@ -1,10 +1,8 @@
 'use strict';
 
-const withCallback = require('./Promise');
 const api = 'sending-domains';
 
 module.exports = function(client) {
-
   return {
     /**
      * Lists all sending domains
@@ -17,7 +15,7 @@ module.exports = function(client) {
         uri: api
       };
 
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
 
     /**
@@ -29,14 +27,14 @@ module.exports = function(client) {
      */
     get: function(domain, callback) {
       if (!domain || typeof domain === 'function') {
-        return withCallback(Promise.reject(new Error('domain is required')), callback);
+        return client.reject(new Error('domain is required'), callback);
       }
 
       const options = {
         uri: `${api}/${domain}`
       };
 
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
 
     /**
@@ -48,7 +46,7 @@ module.exports = function(client) {
      */
     create: function(createOpts, callback) {
       if (!createOpts || typeof createOpts !== 'object') {
-        return withCallback(Promise.reject(new Error('create options are required')), callback);
+        return client.reject(new Error('create options are required'), callback);
       }
 
       const options = {
@@ -56,7 +54,7 @@ module.exports = function(client) {
         json: createOpts
       };
 
-      return withCallback(client.post(options), callback);
+      return client.post(options, callback);
     },
 
     /**
@@ -69,11 +67,11 @@ module.exports = function(client) {
      */
     update: function(domain, updateOpts, callback) {
       if (typeof domain !== 'string') {
-        return withCallback(Promise.reject(new Error('domain is required')), callback);
+        return client.reject(new Error('domain is required'), callback);
       }
 
       if (!updateOpts || typeof updateOpts !== 'object') {
-        return withCallback(Promise.reject(new Error('update options are required')), callback);
+        return client.reject(new Error('update options are required'), callback);
       }
 
       const options = {
@@ -81,7 +79,7 @@ module.exports = function(client) {
         json: updateOpts
       };
 
-      return withCallback(client.put(options), callback);
+      return client.put(options, callback);
     },
 
     /**
@@ -93,14 +91,14 @@ module.exports = function(client) {
      */
     delete: function(domain, callback) {
       if (typeof domain !== 'string') {
-        return withCallback(Promise.reject(new Error('domain is required')), callback);
+        return client.reject(new Error('domain is required'), callback);
       }
 
       const options = {
         uri: `${api}/${domain}`
       };
 
-      return withCallback(client.delete(options), callback);
+      return client.delete(options, callback);
     },
 
     /**
@@ -113,11 +111,11 @@ module.exports = function(client) {
      */
     verify: function(domain, options, callback) {
       if (typeof domain !== 'string') {
-        return withCallback(Promise.reject(new Error('domain is required')), callback);
+        return client.reject(new Error('domain is required'), callback);
       }
 
       if (!options || typeof options !== 'object') {
-        return withCallback(Promise.reject(new Error('verification options are required')), callback);
+        return client.reject(new Error('verification options are required'), callback);
       }
 
       const reqOpts = {
@@ -125,7 +123,7 @@ module.exports = function(client) {
         json: options
       };
 
-      return withCallback(client.post(reqOpts), callback);
+      return client.post(reqOpts, callback);
     }
   };
 
diff --git a/lib/sparkpost.js b/lib/sparkpost.js
index 9f85293..5e28754 100644
--- a/lib/sparkpost.js
+++ b/lib/sparkpost.js
@@ -2,7 +2,7 @@
 
 const version = require('../package.json').version;
 const url = require('url');
-const withCallback = require('./Promise');
+const withCallback = require('./withCallback');
 const request = require('request');
 const _ = require('lodash');
 
@@ -141,25 +141,29 @@ SparkPost.prototype.get = function(options, callback) {
   options.method = 'GET';
   options.json = true;
 
-  return withCallback(this.request(options), callback);
+  return this.request(options, callback);
 };
 
 SparkPost.prototype.post = function(options, callback) {
   options.method = 'POST';
 
-  return withCallback(this.request(options), callback);
+  return this.request(options, callback);
 };
 
 SparkPost.prototype.put = function(options, callback) {
   options.method = 'PUT';
 
-  return withCallback(this.request(options), callback);
+  return this.request(options, callback);
 };
 
 SparkPost.prototype.delete = function(options, callback) {
   options.method = 'DELETE';
 
-  return withCallback(this.request(options), callback);
+  return this.request(options, callback);
+};
+
+SparkPost.prototype.reject = function(error, callback) {
+  return withCallback(Promise.reject(error), callback);
 };
 
 module.exports = SparkPost;
diff --git a/lib/subaccounts.js b/lib/subaccounts.js
index ab004e8..15546ba 100644
--- a/lib/subaccounts.js
+++ b/lib/subaccounts.js
@@ -1,6 +1,5 @@
 'use strict';
 
-const withCallback = require('./Promise');
 const api = 'subaccounts';
 
 module.exports = function(client) {
@@ -15,7 +14,7 @@ module.exports = function(client) {
       const options = {
         uri: api
       };
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
     /**
      * Get details about a specified subaccount by its id
@@ -26,13 +25,13 @@ module.exports = function(client) {
      */
     get: function(id, callback) {
       if (!id || typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       const options = {
         uri: `${api}/${id}`
       };
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
     /**
      * Create a new subaccount
@@ -43,14 +42,14 @@ module.exports = function(client) {
      */
     create: function(subaccount, callback) {
       if (!subaccount || typeof subaccount !== 'object') {
-        return withCallback(Promise.reject(new Error('subaccount object is required')), callback);
+        return client.reject(new Error('subaccount object is required'), callback);
       }
 
       const reqOpts = {
         uri: api,
         json: subaccount
       };
-      return withCallback(client.post(reqOpts), callback);
+      return client.post(reqOpts, callback);
     },
     /**
      * Update existing subaccount by id
@@ -62,11 +61,11 @@ module.exports = function(client) {
      */
     update: function(id, subaccount, callback) {
       if (!id || typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       if (!subaccount || typeof subaccount !== 'object') {
-        return withCallback(Promise.reject(new Error('subaccount object is required')), callback);
+        return client.reject(new Error('subaccount object is required'), callback);
       }
 
       const reqOpts = {
@@ -74,7 +73,7 @@ module.exports = function(client) {
         json: subaccount
       };
 
-      return withCallback(client.put(reqOpts), callback);
+      return client.put(reqOpts, callback);
     }
   };
 
diff --git a/lib/suppressionList.js b/lib/suppressionList.js
index 2ea71bc..f683a11 100644
--- a/lib/suppressionList.js
+++ b/lib/suppressionList.js
@@ -1,6 +1,5 @@
 'use strict';
 
-const withCallback = require('./Promise');
 const api = 'suppression-list';
 
 module.exports = function(client) {
@@ -19,7 +18,7 @@ module.exports = function(client) {
         uri: api
         , qs: parameters
       };
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
 
     /**
@@ -31,13 +30,13 @@ module.exports = function(client) {
      */
     get: function(email, callback) {
       if (!email || typeof email === 'function') {
-        return withCallback(Promise.reject(new Error('email is required')), callback);
+        return client.reject(new Error('email is required'), callback);
       }
 
       const options = {
         uri: `${api}/${email}`
       };
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
 
     /**
@@ -50,7 +49,7 @@ module.exports = function(client) {
      */
     upsert: function(listEntries, callback) {
       if (!listEntries || typeof listEntries === 'function') {
-        return withCallback(Promise.reject(new Error('list entries is required')), callback);
+        return client.reject(new Error('list entries is required'), callback);
       }
 
       if (!Array.isArray(listEntries)) {
@@ -62,7 +61,7 @@ module.exports = function(client) {
         json: { recipients: listEntries }
       };
 
-      return withCallback(client.put(options, callback), callback);
+      return client.put(options, callback);
     },
 
     /**
@@ -74,13 +73,13 @@ module.exports = function(client) {
      */
     delete: function(email, callback) {
       if (!email || typeof email === 'function') {
-        return withCallback(Promise.reject(new Error('email is required')), callback);
+        return client.reject(new Error('email is required'), callback);
       }
 
       const options = {
         uri: `${api}/${email}`
       };
-      return withCallback(client.delete(options), callback);
+      return client.delete(options, callback);
     }
   };
 
diff --git a/lib/templates.js b/lib/templates.js
index a2d0f81..a7b2b9f 100644
--- a/lib/templates.js
+++ b/lib/templates.js
@@ -1,6 +1,5 @@
 'use strict';
 
-const withCallback = require('./Promise');
 const api = 'templates';
 
 const _ = require('lodash');
@@ -17,7 +16,7 @@ module.exports = function(client) {
       const options = {
         uri: api
       };
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
     /**
      * Get details about a specified template by its id.
@@ -36,7 +35,7 @@ module.exports = function(client) {
       }
 
       if (!id) {
-        return withCallback(Promise.reject(new Error('template id is required')), callback);
+        return client.reject(new Error('template id is required'), callback);
       }
 
       const reqOpts = {
@@ -44,7 +43,7 @@ module.exports = function(client) {
         , qs: options
       };
 
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     },
     /**
      * Create a new template.
@@ -55,7 +54,7 @@ module.exports = function(client) {
      */
     create: function(template, callback) {
       if (!template || typeof template !== 'object') {
-        return withCallback(Promise.reject(new Error('template object is required')), callback);
+        return client.reject(new Error('template object is required'), callback);
       }
 
       const reqOpts = {
@@ -63,7 +62,7 @@ module.exports = function(client) {
         , json: template
       };
 
-      return withCallback(client.post(reqOpts), callback);
+      return client.post(reqOpts, callback);
     },
     /**
      * Update an existing template.
@@ -82,11 +81,11 @@ module.exports = function(client) {
       }
 
       if (!id) {
-        return withCallback(Promise.reject(new Error('template id is required')), callback);
+        return client.reject(new Error('template id is required'), callback);
       }
 
       if (!template || typeof template !== 'object') {
-        return withCallback(Promise.reject(new Error('template object is required')), callback);
+        return client.reject(new Error('template object is required'), callback);
       }
 
       const reqOpts = {
@@ -95,7 +94,7 @@ module.exports = function(client) {
         , qs: options
       };
 
-      return withCallback(client.put(reqOpts), callback);
+      return client.put(reqOpts, callback);
     },
     /**
      * Delete an existing template.
@@ -106,13 +105,13 @@ module.exports = function(client) {
      */
     delete: function(id, callback) {
       if (!id || typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('template id is required')), callback);
+        return client.reject(new Error('template id is required'), callback);
       }
 
       const options = {
         uri: `${api}/${id}`
       };
-      return withCallback(client.delete(options), callback);
+      return client.delete(options, callback);
     },
     /**
      * Preview the most recent version of an existing template by id.
@@ -132,7 +131,7 @@ module.exports = function(client) {
       }
 
       if (!id) {
-        return withCallback(Promise.reject(new Error('template id is required')), callback);
+        return client.reject(new Error('template id is required'), callback);
       }
 
       const reqOpts = {
@@ -146,7 +145,7 @@ module.exports = function(client) {
         delete reqOpts.json.draft;
       }
 
-      return withCallback(client.post(reqOpts), callback);
+      return client.post(reqOpts, callback);
     }
   };
 };
diff --git a/lib/transmissions.js b/lib/transmissions.js
index 74e1a85..084c9f8 100644
--- a/lib/transmissions.js
+++ b/lib/transmissions.js
@@ -1,7 +1,6 @@
 'use strict';
 
 const _ = require('lodash');
-const withCallback = require('./Promise');
 const api = 'transmissions';
 
 /*
@@ -10,7 +9,6 @@ const api = 'transmissions';
  * info about a specific transmission
  */
 module.exports = function(client) {
-
   return {
     /**
      * List an overview of all transmissions in the account
@@ -31,7 +29,7 @@ module.exports = function(client) {
         qs: options
       };
 
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     },
     /**
      * Retrieve the details about a transmission by its id
@@ -42,14 +40,14 @@ module.exports = function(client) {
      */
     get: function(id, callback) {
       if (typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       const options = {
         uri: `${api}/${id}`
       };
 
-      return withCallback(client.get(options), callback);
+      return client.get(options, callback);
     },
     /**
      * Sends a message by creating a new transmission
@@ -67,7 +65,7 @@ module.exports = function(client) {
       }
 
       if (!transmission || typeof transmission !== 'object') {
-        return withCallback(Promise.reject(new Error('transmission object is required')), callback);
+        return client.reject(new Error('transmission object is required'), callback);
       }
 
       transmission = formatPayload(transmission);
@@ -78,7 +76,7 @@ module.exports = function(client) {
         qs: options
       };
 
-      return withCallback(client.post(reqOpts), callback);
+      return client.post(reqOpts, callback);
     }
   };
 
diff --git a/lib/webhooks.js b/lib/webhooks.js
index 47d8cbc..d6f46d6 100644
--- a/lib/webhooks.js
+++ b/lib/webhooks.js
@@ -1,6 +1,5 @@
 'use strict';
 
-const withCallback = require('./Promise');
 const api = 'webhooks';
 
 module.exports = function(client) {
@@ -29,7 +28,7 @@ module.exports = function(client) {
         reqOpts.qs.timezone = options.timezone;
       }
 
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     },
 
     /**
@@ -48,7 +47,7 @@ module.exports = function(client) {
       }
 
       if (typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       const reqOpts = {
@@ -60,7 +59,7 @@ module.exports = function(client) {
         reqOpts.qs.timezone = options.timezone;
       }
 
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     },
 
     /**
@@ -72,7 +71,7 @@ module.exports = function(client) {
      */
     create: function(webhook, callback) {
       if (!webhook || typeof webhook === 'function') {
-        return withCallback(Promise.reject(new Error('webhook object is required')), callback);
+        return client.reject(new Error('webhook object is required'), callback);
       }
 
       const options = {
@@ -80,7 +79,7 @@ module.exports = function(client) {
         json: webhook
       };
 
-      return withCallback(client.post(options), callback);
+      return client.post(options, callback);
     },
 
     /**
@@ -93,11 +92,11 @@ module.exports = function(client) {
      */
     update: function(id, webhook, callback) {
       if (!id) {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       if (!webhook || typeof webhook === 'function') {
-        return withCallback(Promise.reject(new Error('webhook object is required')), callback);
+        return client.reject(new Error('webhook object is required'), callback);
       }
 
       const options = {
@@ -107,7 +106,7 @@ module.exports = function(client) {
 
       delete options.json.id;
 
-      return withCallback(client.put(options), callback);
+      return client.put(options, callback);
     },
 
     /**
@@ -119,14 +118,14 @@ module.exports = function(client) {
      */
     delete: function(id, callback) {
       if (!id || typeof id === 'function') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       const options = {
         uri: `${api}/${id}`
       };
 
-      return withCallback(client.delete(options), callback);
+      return client.delete(options, callback);
     },
 
     /**
@@ -140,11 +139,11 @@ module.exports = function(client) {
      */
     validate: function(id, options, callback) {
       if (typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       if (!options || typeof options === 'function' || !options.message) {
-        return withCallback(Promise.reject(new Error('message is required')), callback);
+        return client.reject(new Error('message is required'), callback);
       }
 
       const reqOpts = {
@@ -154,7 +153,7 @@ module.exports = function(client) {
         }
       };
 
-      return withCallback(client.post(reqOpts), callback);
+      return client.post(reqOpts, callback);
     },
 
     /**
@@ -173,7 +172,7 @@ module.exports = function(client) {
       }
 
       if (typeof id !== 'string') {
-        return withCallback(Promise.reject(new Error('id is required')), callback);
+        return client.reject(new Error('id is required'), callback);
       }
 
       const reqOpts = {
@@ -185,7 +184,7 @@ module.exports = function(client) {
         reqOpts.qs.limit = options.limit;
       }
 
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     },
 
     /**
@@ -198,7 +197,7 @@ module.exports = function(client) {
       const reqOpts = {
         uri: `${api}/events/documentation`
       };
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     },
 
     /**
@@ -224,7 +223,7 @@ module.exports = function(client) {
         reqOpts.qs.events = options.events;
       }
 
-      return withCallback(client.get(reqOpts), callback);
+      return client.get(reqOpts, callback);
     }
   };
 };
diff --git a/lib/Promise.js b/lib/withCallback.js
similarity index 100%
rename from lib/Promise.js
rename to lib/withCallback.js
diff --git a/test/spec/inboundDomains.spec.js b/test/spec/inboundDomains.spec.js
index ce4b3fe..f9eae93 100644
--- a/test/spec/inboundDomains.spec.js
+++ b/test/spec/inboundDomains.spec.js
@@ -2,6 +2,7 @@
 
 var chai = require('chai')
   , expect = chai.expect
+  , SparkPost = require('../../lib/sparkpost')
   , sinon = require('sinon');
 
 require('sinon-as-promised');
@@ -10,35 +11,42 @@ chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
 
 describe('Inbound Domains Library', function() {
-  let client, inboundDomains;
+  let client, inboundDomains, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({}),
       post: sinon.stub().resolves({}),
-      delete: sinon.stub().resolves({})
+      delete: sinon.stub().resolves({}),
+      reject: SparkPost.prototype.reject
     };
 
+    callback = function() {};
+
     inboundDomains = require('../../lib/inboundDomains')(client);
   });
 
   describe('list Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return inboundDomains.list()
+
+      return inboundDomains.list(callback)
         .then(function() {
           expect(client.get.firstCall.args[0]).to.deep.equal({uri: 'inbound-domains'});
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
   });
 
   describe('get Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return inboundDomains.get('test')
+      return inboundDomains.get('test', callback)
         .then(function() {
           expect(client.get.firstCall.args[0]).to.deep.equal({uri: 'inbound-domains/test'});
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
+
     it('should throw an error if domain is missing', function() {
       return expect(inboundDomains.get()).to.be.rejectedWith('domain is required');
     });
@@ -47,10 +55,11 @@ describe('Inbound Domains Library', function() {
   describe('create Method', function() {
     it('should call client post method with the appropriate uri and payload', function() {
       let createOpts = {domain: 'test'};
-      return inboundDomains.create(createOpts)
+      return inboundDomains.create(createOpts, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('inbound-domains');
           expect(client.post.firstCall.args[0].json).to.deep.equal(createOpts);
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -61,9 +70,10 @@ describe('Inbound Domains Library', function() {
 
   describe('delete Method', function() {
     it('should call client delete method with the appropriate uri', function() {
-      return inboundDomains.delete('test')
+      return inboundDomains.delete('test', callback)
         .then(function () {
           expect(client.delete.firstCall.args[0].uri).to.equal('inbound-domains/test');
+          expect(client.delete.firstCall.args[1]).to.equal(callback);
         });
     });
 
diff --git a/test/spec/messageEvents.spec.js b/test/spec/messageEvents.spec.js
index 5b9fdfc..cfd381b 100644
--- a/test/spec/messageEvents.spec.js
+++ b/test/spec/messageEvents.spec.js
@@ -2,8 +2,7 @@
 
 var chai = require('chai')
   , expect = chai.expect
-  , sinon = require('sinon')
-  , Promise = require('../../lib/Promise');
+  , sinon = require('sinon');
 
 require('sinon-as-promised');
 
@@ -11,13 +10,15 @@ chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
 
 describe('Message Events Library', function() {
-  let client, messageEvents;
+  let client, messageEvents, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({})
     };
 
+    callback = function() {};
+
     messageEvents = require('../../lib/messageEvents')(client);
   });
 
@@ -39,11 +40,12 @@ describe('Message Events Library', function() {
         to: '2016-11-14T16:15',
         transmission_ids: '65832150921904138'
       };
-      return messageEvents.search(options)
+      return messageEvents.search(options, callback)
         .then(function() {
           Object.keys(options).forEach(function(key) {
             expect(client.get.firstCall.args[0].qs).to.have.property(key).and.equal(options[key]);
           });
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
diff --git a/test/spec/recipientLists.spec.js b/test/spec/recipientLists.spec.js
index e0bee3f..af1b261 100644
--- a/test/spec/recipientLists.spec.js
+++ b/test/spec/recipientLists.spec.js
@@ -3,6 +3,7 @@
 var _ = require('lodash')
   , chai = require('chai')
   , expect = chai.expect
+  , SparkPost = require('../../lib/sparkpost')
   , sinon = require('sinon');
 
 require('sinon-as-promised');
@@ -11,36 +12,40 @@ chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
 
 describe('Recipient Lists Library', function() {
-  var client, recipientLists;
+  var client, recipientLists, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({}),
       post: sinon.stub().resolves({}),
       put: sinon.stub().resolves({}),
-      delete: sinon.stub().resolves({})
+      delete: sinon.stub().resolves({}),
+      reject: SparkPost.prototype.reject
     };
 
+    callback = function() {};
+
     recipientLists = require('../../lib/recipientLists')(client);
   });
 
   describe('list', function() {
 
     it('should call client get method with the appropriate uri', function() {
-      return recipientLists.list()
+      return recipientLists.list(callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('recipient-lists');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
-
   });
 
   describe('get', function() {
 
     it('should call client get method with the appropriate uri', function() {
-      return recipientLists.get('test-id')
+      return recipientLists.get('test-id', callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('recipient-lists/test-id');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -50,6 +55,9 @@ describe('Recipient Lists Library', function() {
 
     it('should not throw an error if optional 2nd argument is a function (callback)', function() {
       let cb = sinon.stub();
+
+      client.get.yields();
+
       return recipientLists.get('test-id', cb).then(() => {
         expect(cb.callCount).to.equal(1);
       });
@@ -83,10 +91,11 @@ describe('Recipient Lists Library', function() {
         ]
       };
 
-      return recipientLists.create(testList)
+      return recipientLists.create(testList, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('recipient-lists');
           expect(client.post.firstCall.args[0].json).to.deep.equal(testList);
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -135,10 +144,11 @@ describe('Recipient Lists Library', function() {
       };
       const testId = 'test-id';
 
-      return recipientLists.update(testId, testList)
+      return recipientLists.update(testId, testList, callback)
         .then(function() {
           expect(client.put.firstCall.args[0].uri).to.equal('recipient-lists/' + testId);
           expect(client.put.firstCall.args[0].json).to.deep.equal(testList);
+          expect(client.put.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -174,9 +184,10 @@ describe('Recipient Lists Library', function() {
   describe('delete', function() {
 
     it('should call client delete method with the appropriate uri', function() {
-      return recipientLists.delete('test')
+      return recipientLists.delete('test', callback)
         .then(function() {
           expect(client.delete.firstCall.args[0].uri).to.equal('recipient-lists/test');
+          expect(client.delete.firstCall.args[1]).to.equal(callback);
         });
     });
 
diff --git a/test/spec/relayWebhooks.spec.js b/test/spec/relayWebhooks.spec.js
index 35aaa35..627bbf5 100644
--- a/test/spec/relayWebhooks.spec.js
+++ b/test/spec/relayWebhooks.spec.js
@@ -2,6 +2,7 @@
 
 var chai = require('chai')
   , expect = chai.expect
+  , SparkPost = require('../../lib/sparkpost')
   , sinon = require('sinon');
 
 require('sinon-as-promised');
@@ -10,33 +11,38 @@ chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
 
 describe('Relay Webhooks Library', function() {
-  let client, relayWebhooks;
+  let client, relayWebhooks, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({}),
       post: sinon.stub().resolves({}),
       put: sinon.stub().resolves({}),
-      delete: sinon.stub().resolves({})
+      delete: sinon.stub().resolves({}),
+      reject: SparkPost.prototype.reject
     };
 
+    callback = function() {};
+
     relayWebhooks = require('../../lib/relayWebhooks')(client);
   });
 
   describe('list Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return relayWebhooks.list()
+      return relayWebhooks.list(callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('relay-webhooks');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
   });
 
   describe('get Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return relayWebhooks.get('test')
+      return relayWebhooks.get('test', callback)
         .then(function() {
           expect(client.get.firstCall.args[0]).to.deep.equal({uri: 'relay-webhooks/test'});
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -52,10 +58,11 @@ describe('Relay Webhooks Library', function() {
         domain: 'inbound.example.com'
       };
 
-      return relayWebhooks.create(webhook)
+      return relayWebhooks.create(webhook, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('relay-webhooks');
           expect(client.post.firstCall.args[0].json).to.deep.equal(webhook);
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -70,10 +77,11 @@ describe('Relay Webhooks Library', function() {
         name: 'New Replies Webhook'
       };
 
-      return relayWebhooks.update('test', webhook)
+      return relayWebhooks.update('test', webhook, callback)
         .then(function() {
           expect(client.put.firstCall.args[0].uri).to.equal('relay-webhooks/test');
           expect(client.put.firstCall.args[0].json).to.deep.equal(webhook);
+          expect(client.put.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -88,9 +96,10 @@ describe('Relay Webhooks Library', function() {
 
   describe('delete Method', function() {
     it('should call client delete method with the appropriate uri', function() {
-      return relayWebhooks.delete('test')
+      return relayWebhooks.delete('test', callback)
         .then(function() {
           expect(client.delete.firstCall.args[0].uri).to.equal('relay-webhooks/test');
+          expect(client.delete.firstCall.args[1]).to.equal(callback);
         });
     });
 
diff --git a/test/spec/sendingDomains.spec.js b/test/spec/sendingDomains.spec.js
index e8d3aa7..2989651 100644
--- a/test/spec/sendingDomains.spec.js
+++ b/test/spec/sendingDomains.spec.js
@@ -3,6 +3,7 @@
 var _ = require('lodash')
   , chai = require('chai')
   , expect = chai.expect
+  , SparkPost = require('../../lib/sparkpost')
   , sinon = require('sinon');
 
 require('sinon-as-promised');
@@ -11,33 +12,38 @@ chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
 
 describe('Sending Domains Library', function() {
-  var client, sendingDomains;
+  var client, sendingDomains, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({}),
       post: sinon.stub().resolves({}),
       put: sinon.stub().resolves({}),
-      delete: sinon.stub().resolves({})
+      delete: sinon.stub().resolves({}),
+      reject: SparkPost.prototype.reject
     };
 
+    callback = function() {};
+
     sendingDomains = require('../../lib/sendingDomains')(client);
   });
 
   describe('list', function() {
     it('should call client get method with the appropriate uri', function() {
-      return sendingDomains.list()
+      return sendingDomains.list(callback)
         .then(function() {
           expect(client.get.firstCall.args[0]).to.deep.equal({uri: 'sending-domains'});
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
   });
 
   describe('get', function() {
     it('should call client get method with the appropriate uri', function() {
-      return sendingDomains.get('test')
+      return sendingDomains.get('test', callback)
         .then(function() {
           expect(client.get.firstCall.args[0]).to.deep.equal({uri: 'sending-domains/test'});
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -52,9 +58,10 @@ describe('Sending Domains Library', function() {
         domain: 'test'
       };
 
-      return sendingDomains.create(sendingDomain).then(function() {
+      return sendingDomains.create(sendingDomain, callback).then(function() {
         expect(client.post.firstCall.args[0].uri).to.equal('sending-domains');
         expect(client.post.firstCall.args[0].json).to.deep.equal(sendingDomain);
+        expect(client.post.firstCall.args[1]).to.equal(callback);
       });
     });
 
@@ -69,10 +76,11 @@ describe('Sending Domains Library', function() {
         tracking_domain: 'click.example1.com'
       };
 
-      return sendingDomains.update('test', sendingDomain)
+      return sendingDomains.update('test', sendingDomain, callback)
         .then(function() {
           expect(client.put.firstCall.args[0].uri).to.equal('sending-domains/test');
           expect(client.put.firstCall.args[0].json).to.deep.equal(_.omit(sendingDomain, 'domain'));
+          expect(client.put.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -87,9 +95,10 @@ describe('Sending Domains Library', function() {
 
   describe('delete', function() {
     it('should call client delete method with the appropriate uri', function() {
-      return sendingDomains.delete('test')
+      return sendingDomains.delete('test', callback)
         .then(function() {
           expect(client.delete.firstCall.args[0].uri).to.equal('sending-domains/test');
+          expect(client.delete.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -105,10 +114,11 @@ describe('Sending Domains Library', function() {
         spf_verify: true
       };
 
-      return sendingDomains.verify('test', options)
+      return sendingDomains.verify('test', options, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('sending-domains/test/verify');
           expect(client.post.firstCall.args[0].json).to.deep.equal(_.omit(options, 'domain'));
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -120,5 +130,5 @@ describe('Sending Domains Library', function() {
       return expect(sendingDomains.verify('test')).to.be.rejectedWith('verification options are required');
     });
   });
-  
+
 });
diff --git a/test/spec/subaccounts.spec.js b/test/spec/subaccounts.spec.js
index b4cec81..87b7cf1 100644
--- a/test/spec/subaccounts.spec.js
+++ b/test/spec/subaccounts.spec.js
@@ -2,6 +2,7 @@
 
 var chai = require('chai')
   , expect = chai.expect
+  , SparkPost = require('../../lib/sparkpost')
   , sinon = require('sinon');
 
 require('sinon-as-promised');
@@ -10,32 +11,37 @@ chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
 
 describe('Subaccounts Library', function() {
-  let client, subaccounts;
+  let client, subaccounts, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({}),
       post: sinon.stub().resolves({}),
-      put: sinon.stub().resolves({})
+      put: sinon.stub().resolves({}),
+      reject: SparkPost.prototype.reject
     };
 
+    callback = function() {};
+
     subaccounts = require('../../lib/subaccounts')(client);
   });
 
   describe('list Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return subaccounts.list()
+      return subaccounts.list(callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('subaccounts');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
   });
 
   describe('get Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return subaccounts.get('test')
+      return subaccounts.get('test', callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('subaccounts/test');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -52,10 +58,11 @@ describe('Subaccounts Library', function() {
         key_grants: []
       };
 
-      return subaccounts.create(subaccount)
+      return subaccounts.create(subaccount, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('subaccounts');
           expect(client.post.firstCall.args[0].json).to.deep.equal(subaccount);
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -72,10 +79,11 @@ describe('Subaccounts Library', function() {
         ip_pool: ''
       };
 
-      return subaccounts.update('test', subaccount)
+      return subaccounts.update('test', subaccount, callback)
         .then(function() {
           expect(client.put.firstCall.args[0].uri).to.equal('subaccounts/test');
           expect(client.put.firstCall.args[0].json).to.deep.equal(subaccount);
+          expect(client.put.firstCall.args[1]).to.equal(callback);
         });
     });
 
diff --git a/test/spec/suppressionList.spec.js b/test/spec/suppressionList.spec.js
index f28be3b..db01e02 100644
--- a/test/spec/suppressionList.spec.js
+++ b/test/spec/suppressionList.spec.js
@@ -2,6 +2,7 @@
 
 var chai = require('chai')
   , expect = chai.expect
+  , SparkPost = require('../../lib/sparkpost')
   , sinon = require('sinon');
 
 require('sinon-as-promised');
@@ -10,33 +11,38 @@ chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
 
 describe('Suppression List Library', function() {
-  let client, suppressionList;
+  let client, suppressionList, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({}),
       post: sinon.stub().resolves({}),
       put: sinon.stub().resolves({}),
-      delete: sinon.stub().resolves({})
+      delete: sinon.stub().resolves({}),
+      reject: SparkPost.prototype.reject
     };
 
+    callback = function() {};
+
     suppressionList = require('../../lib/suppressionList')(client);
   });
 
   describe('list', function() {
     it('should call client get method with the appropriate uri', function() {
-      return suppressionList.list({limit: 5})
+      return suppressionList.list({limit: 5}, callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('suppression-list');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
   });
 
   describe('get', function() {
     it('should call client get method with the appropriate uri', function() {
-      return suppressionList.get('test@test.com')
+      return suppressionList.get('test@test.com', callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('suppression-list/test@test.com');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -49,10 +55,11 @@ describe('Suppression List Library', function() {
     it('should accept a single list entry', function() {
       var listEntry = { email: 'test@test.com' };
 
-      return suppressionList.upsert(listEntry)
+      return suppressionList.upsert(listEntry, callback)
         .then(function() {
           expect(client.put.firstCall.args[0].uri).to.equal('suppression-list');
           expect(client.put.firstCall.args[0].json.recipients).to.deep.equal([listEntry]);
+          expect(client.put.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -76,9 +83,10 @@ describe('Suppression List Library', function() {
 
   describe('delete', function() {
     it('should call client delete method with the appropriate uri', function() {
-      return suppressionList.delete('test@test.com')
+      return suppressionList.delete('test@test.com', callback)
         .then(function() {
           expect(client.delete.firstCall.args[0].uri).to.equal('suppression-list/test@test.com');
+          expect(client.delete.firstCall.args[1]).to.equal(callback);
         });
     });
 
diff --git a/test/spec/templates.spec.js b/test/spec/templates.spec.js
index 82cbb30..c419a13 100644
--- a/test/spec/templates.spec.js
+++ b/test/spec/templates.spec.js
@@ -1,8 +1,8 @@
 'use strict';
-
 var _ = require('lodash')
   , chai = require('chai')
   , expect = chai.expect
+  , SparkPost = require('../../lib/sparkpost')
   , sinon = require('sinon');
 
 require('sinon-as-promised');
@@ -11,24 +11,28 @@ chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
 
 describe('Templates Library', function() {
-  var client, templates;
+  var client, templates, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({}),
       post: sinon.stub().resolves({}),
       put: sinon.stub().resolves({}),
-      delete: sinon.stub().resolves({})
+      delete: sinon.stub().resolves({}),
+      reject: SparkPost.prototype.reject
     };
 
+    callback = function() {};
+
     templates = require('../../lib/templates')(client);
   });
 
   describe('list Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return templates.list()
+      return templates.list(callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('templates');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
   });
@@ -36,9 +40,10 @@ describe('Templates Library', function() {
   describe('get Method', function() {
     it('should call client get method with the appropriate uri', function() {
       var id = 'test';
-      return templates.get(id)
+      return templates.get(id, callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('templates/test');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -58,15 +63,6 @@ describe('Templates Library', function() {
           expect(client.get.firstCall.args[0].qs).to.deep.equal({draft: true});
         });
     });
-
-    it('should work given just an id and callback', function() {
-      var id = 'test';
-
-      return templates.get(id, function() {
-        expect(client.get.firstCall.args[0].uri).to.contain(id);
-        expect(client.get.firstCall.args[0].qs).to.deep.equal({});
-      });
-    });
   });
 
   describe('create Method', function() {
@@ -75,10 +71,11 @@ describe('Templates Library', function() {
         id: 'test'
       };
 
-      return templates.create(template)
+      return templates.create(template, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('templates');
           expect(client.post.firstCall.args[0].json).to.deep.equal(template);
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -94,10 +91,11 @@ describe('Templates Library', function() {
           name: 'A new name!'
         };
 
-      return templates.update(id, template)
+      return templates.update(id, template, callback)
         .then(function() {
           expect(client.put.firstCall.args[0].uri).to.equal('templates/test');
           expect(client.put.firstCall.args[0].json).to.deep.equal(template);
+          expect(client.put.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -115,6 +113,9 @@ describe('Templates Library', function() {
         , template = {
           name: 'A new name!'
         };
+
+      client.put.yields();
+
       return templates.update(id, template, cb).then(function() {
         expect(cb.callCount).to.equal(1);
       });
@@ -138,9 +139,10 @@ describe('Templates Library', function() {
 
   describe('delete Method', function() {
     it('should call client delete method with the appropriate uri', function() {
-      return templates.delete('test')
+      return templates.delete('test', callback)
         .then(function() {
           expect(client.delete.firstCall.args[0].uri).to.equal('templates/test');
+          expect(client.delete.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -159,10 +161,11 @@ describe('Templates Library', function() {
             'member': true
           }
         };
-      return templates.preview(id, options)
+      return templates.preview(id, options, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('templates/test/preview');
           expect(client.post.firstCall.args[0].json).to.deep.equal(options);
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -172,6 +175,9 @@ describe('Templates Library', function() {
 
     it('should not throw an error if optional 2nd argument is a function (callback)', function() {
       let cb = sinon.stub();
+
+      client.post.yields();
+
       return templates.preview('test', cb).then(function() {
         expect(cb.callCount).to.equal(1);
       });
diff --git a/test/spec/transmissions.spec.js b/test/spec/transmissions.spec.js
index 71dd5f2..fbc5011 100644
--- a/test/spec/transmissions.spec.js
+++ b/test/spec/transmissions.spec.js
@@ -2,13 +2,13 @@
 
 var chai = require('chai')
   , expect = chai.expect
+  , SparkPost = require('../../lib/sparkpost')
   , sinon = require('sinon');
 
 require('sinon-as-promised');
 
 chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
-
 var ccTransmission = {
     recipients: [
       {
@@ -83,32 +83,29 @@ var ccTransmission = {
   , expectedCCHeader = '"John" <cc1@gmail.com>, "Jane" <cc2@gmail.com>';
 
 describe('Transmissions Library', function() {
-  var client, transmissions;
+  var client, transmissions, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({}),
-      post: sinon.stub().resolves({})
+      post: sinon.stub().resolves({}),
+      reject: SparkPost.prototype.reject
     };
 
+    callback = function() {};
+
     transmissions = require('../../lib/transmissions')(client);
   });
 
-  describe('all Method', function() {
+  describe('list Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return transmissions.list()
+      return transmissions.list(callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('transmissions');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
-    it('should call client get method with the appropriate uri using callback', function(done) {
-      transmissions.list(function() {
-        expect(client.get.firstCall.args[0].uri).to.equal('transmissions');
-        done();
-      });
-    });
-
     it('should allow campaign_id to be set in options', function() {
       var options = {
         campaign_id: 'test-campaign'
@@ -134,9 +131,10 @@ describe('Transmissions Library', function() {
 
   describe('find Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return transmissions.get('test')
+      return transmissions.get('test', callback)
         .then(function() {
           expect(client.get.firstCall.args[0]).to.deep.equal({uri: 'transmissions/test'});
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -151,10 +149,11 @@ describe('Transmissions Library', function() {
         campaign_id: 'test-campaign'
       };
 
-      return transmissions.send(transmission)
+      return transmissions.send(transmission, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('transmissions');
           expect(client.post.firstCall.args[0].json).to.deep.equal(transmission);
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -181,6 +180,9 @@ describe('Transmissions Library', function() {
         , transmission = {
           campaign_id: 'test-campaign'
         };
+
+      client.post.yields();
+
       return transmissions.send(transmission, cb).then(function() {
         expect(cb.callCount).to.equal(1);
       });
diff --git a/test/spec/webhooks.spec.js b/test/spec/webhooks.spec.js
index 2f79d49..b0d82c7 100644
--- a/test/spec/webhooks.spec.js
+++ b/test/spec/webhooks.spec.js
@@ -3,6 +3,7 @@
 var _ = require('lodash')
   , chai = require('chai')
   , expect = chai.expect
+  , SparkPost = require('../../lib/sparkpost')
   , sinon = require('sinon');
 
 require('sinon-as-promised');
@@ -11,24 +12,28 @@ chai.use(require('sinon-chai'));
 chai.use(require('chai-as-promised'));
 
 describe('Webhooks Library', function() {
-  var client, webhooks;
+  var client, webhooks, callback;
 
   beforeEach(function() {
     client = {
       get: sinon.stub().resolves({}),
       post: sinon.stub().resolves({}),
       put: sinon.stub().resolves({}),
-      delete: sinon.stub().resolves({})
+      delete: sinon.stub().resolves({}),
+      reject: SparkPost.prototype.reject
     };
 
+    callback = function() {};
+
     webhooks = require('../../lib/webhooks')(client);
   });
 
   describe('list Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return webhooks.list()
+      return webhooks.list(callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('webhooks');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -46,9 +51,10 @@ describe('Webhooks Library', function() {
 
   describe('get Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return webhooks.get('test')
+      return webhooks.get('test', callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('webhooks/test');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -76,10 +82,11 @@ describe('Webhooks Library', function() {
         events: ['delivery', 'injection', 'open', 'click']
       };
 
-      return webhooks.create(webhook)
+      return webhooks.create(webhook, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('webhooks');
           expect(client.post.firstCall.args[0].json).to.deep.equal(webhook);
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -96,10 +103,11 @@ describe('Webhooks Library', function() {
         auth_type: 'none'
       };
 
-      return webhooks.update('test', webhook)
+      return webhooks.update('test', webhook, callback)
         .then(function() {
           expect(client.put.firstCall.args[0].uri).to.equal('webhooks/test');
           expect(client.put.firstCall.args[0].json).to.deep.equal(webhook);
+          expect(client.put.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -114,9 +122,10 @@ describe('Webhooks Library', function() {
 
   describe('delete Method', function() {
     it('should call client delete method with the appropriate uri', function() {
-      return webhooks.delete('test')
+      return webhooks.delete('test', callback)
         .then(function() {
           expect(client.delete.firstCall.args[0].uri).to.equal('webhooks/test');
+          expect(client.delete.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -133,10 +142,11 @@ describe('Webhooks Library', function() {
         }
       };
 
-      return webhooks.validate('test', options)
+      return webhooks.validate('test', options, callback)
         .then(function() {
           expect(client.post.firstCall.args[0].uri).to.equal('webhooks/test/validate');
           expect(client.post.firstCall.args[0].json).to.deep.equal(options);
+          expect(client.post.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -151,9 +161,10 @@ describe('Webhooks Library', function() {
 
   describe('getBatchStatus Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return webhooks.getBatchStatus('test')
+      return webhooks.getBatchStatus('test', callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('webhooks/test/batch-status');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
 
@@ -175,18 +186,20 @@ describe('Webhooks Library', function() {
 
   describe('getDocumentation Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return webhooks.getDocumentation()
+      return webhooks.getDocumentation(callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('webhooks/events/documentation');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });
   });
 
   describe('getSamples Method', function() {
     it('should call client get method with the appropriate uri', function() {
-      return webhooks.getSamples()
+      return webhooks.getSamples(callback)
         .then(function() {
           expect(client.get.firstCall.args[0].uri).to.equal('webhooks/events/samples');
+          expect(client.get.firstCall.args[1]).to.equal(callback);
         });
     });