diff --git a/.eslintrc b/.eslintrc
index ed20e71b..5ce15861 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -6,7 +6,7 @@
   },
   "extends": "eslint:recommended",
   "rules": {
-    "strict": "error",
+    "strict": "off",
     "callback-return": "warn",
     "global-require": "error",
     "new-cap": "warn",
diff --git a/test/errors.spec.js b/test/errors.spec.js
index 2b40018f..920db12c 100644
--- a/test/errors.spec.js
+++ b/test/errors.spec.js
@@ -77,7 +77,7 @@ describe('Error handling', () => {
     it('should fail gracefully if an error is thrown inside the configuration function', function (done) {
       this.slow(200);
       let error;
-      storage = GridFsStorage({
+      storage = new GridFsStorage({
         url: settings.mongoUrl,
         file: () => {
           throw new Error('Error thrown');
@@ -106,7 +106,7 @@ describe('Error handling', () => {
     it('should fail gracefully if an error is thrown inside a generator function', function (done) {
       let error;
 
-      storage = GridFsStorage({
+      storage = new GridFsStorage({
         url: settings.mongoUrl,
         file: function* () { // eslint-disable-line require-yield
           throw new Error('File error');
@@ -147,7 +147,7 @@ describe('Error handling', () => {
           setTimeout(() => reject(error), 200);
         });
 
-        storage = GridFsStorage({db: promise});
+        storage = new GridFsStorage({db: promise});
 
         const upload = multer({storage});
 
@@ -190,7 +190,7 @@ describe('Error handling', () => {
             return db.close().then(() => db);
           })
           .then(db => {
-            storage = GridFsStorage({db});
+            storage = new GridFsStorage({db});
             const upload = multer({storage});
 
             app.post('/close', upload.array('photos', 2), (err, req, res, next) => {
@@ -230,7 +230,7 @@ describe('Error handling', () => {
       it('should throw an error if the mongodb connection fails', function (done) {
         const connectionSpy = sinon.spy();
 
-        storage = GridFsStorage({
+        storage = new GridFsStorage({
           url: settings.mongoUrl,
         });
 
@@ -262,7 +262,7 @@ describe('Error handling', () => {
           throw generatedError;
         });
 
-      storage = GridFsStorage({
+      storage = new GridFsStorage({
         url: settings.mongoUrl,
       });
 
diff --git a/test/generators.spec.js b/test/generators.spec.js
index 8ff9e285..e83ed3dd 100644
--- a/test/generators.spec.js
+++ b/test/generators.spec.js
@@ -109,7 +109,7 @@ describe('ES6 generators', () => {
     before((done) => {
       parameters = [];
 
-      storage = GridFsStorage({
+      storage = new GridFsStorage({
         url: setting.mongoUrl,
         file: function* (req, file) {
           let counter = 0;
@@ -161,7 +161,7 @@ describe('ES6 generators', () => {
   describe('promises and generators', () => {
     let result;
     before((done) => {
-      storage = GridFsStorage({
+      storage = new GridFsStorage({
         url: setting.mongoUrl,
         file: function* () {
           let counter = 0;
@@ -240,7 +240,7 @@ describe('ES6 generators', () => {
   describe('finite generators', () => {
     let error;
     before((done) => {
-      storage = GridFsStorage({
+      storage = new GridFsStorage({
         url: setting.mongoUrl,
         file: function* () {
           yield {
@@ -291,7 +291,7 @@ describe('ES6 generators', () => {
   describe('rejected promise', () => {
     let error;
     before((done) => {
-      storage = GridFsStorage({
+      storage = new GridFsStorage({
         url: setting.mongoUrl,
         file: function* () {
           yield Promise.reject('reason');
diff --git a/test/legacy.spec.js b/test/legacy.spec.js
index 96f952dc..a766c565 100644
--- a/test/legacy.spec.js
+++ b/test/legacy.spec.js
@@ -241,7 +241,7 @@ describe('Backwards compatibility', () => {
           },
         }),
       });
-      storage = GridFsStorage({url: setting.mongoUrl});
+      storage = new GridFsStorage({url: setting.mongoUrl});
       storage._legacy = true;
       storage.on('streamError', errorSpy);
       storage.on('file', fileSpy);
@@ -280,7 +280,7 @@ describe('Backwards compatibility', () => {
     before((done) => {
       emitterStub = sinon.stub().callsFake((evt, cb) => {
         if (evt === 'end') {
-          cb();
+          return cb();
         }
       });
       sinon.stub(mongo, 'GridStore').returns({
@@ -292,7 +292,7 @@ describe('Backwards compatibility', () => {
           },
         }),
       });
-      storage = GridFsStorage({url: setting.mongoUrl});
+      storage = new GridFsStorage({url: setting.mongoUrl});
       storage._legacy = true;
       storage.on('streamError', errorSpy);
       storage.on('file', fileSpy);
@@ -342,7 +342,7 @@ describe('Backwards compatibility', () => {
         }
         return Promise.resolve(db);
       });
-      storage = GridFsStorage({url: setting.mongoUrl});
+      storage = new GridFsStorage({url: setting.mongoUrl});
 
       storage.on('connection', (db, client) => {
         expect(db).to.be.an.instanceOf(mongo.Db);
@@ -364,7 +364,7 @@ describe('Backwards compatibility', () => {
         }
         return Promise.resolve(client);
       });
-      storage = GridFsStorage({url: setting.mongoUrl});
+      storage = new GridFsStorage({url: setting.mongoUrl});
 
       storage.on('connection', (db, client) => {
         expect(mongoSpy).to.have.callCount(1);
diff --git a/test/storage.spec.js b/test/storage.spec.js
index 3fa404a6..eea22c2c 100644
--- a/test/storage.spec.js
+++ b/test/storage.spec.js
@@ -639,7 +639,7 @@ describe('Storage', () => {
         },
       });
 
-      storage2 = GridFsStorage({
+      storage2 = new GridFsStorage({
         url: settings.mongoUrl,
         connectionOpts: {
           poolSize: 10,