diff --git a/.rubocop.yml b/.rubocop.yml
index fe81d71..2f54469 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -5,6 +5,8 @@ require:
 AllCops:
   TargetRubyVersion: 2.5
   NewCops: enable
+  Exclude:
+    - prawn-swiss_qr_bill.gemspec
 
 # Prawn is descriptive and needs more branches (methods)
 Metrics/AbcSize:
@@ -21,9 +23,11 @@ RSpec/ExampleLength:
 
 # Unlimited block length for specs
 Metrics/BlockLength:
-  IgnoredMethods: ['describe']
+  AllowedMethods: ['describe']
 
 Lint/AmbiguousBlockAssociation:
   Exclude:
     - 'spec/**/*'
 
+RSpec/NoExpectationExample:
+  Enabled: false
diff --git a/lib/prawn/swiss_qr_bill/qr/data.rb b/lib/prawn/swiss_qr_bill/qr/data.rb
index 565dc76..3dba47e 100644
--- a/lib/prawn/swiss_qr_bill/qr/data.rb
+++ b/lib/prawn/swiss_qr_bill/qr/data.rb
@@ -76,12 +76,12 @@ def initialize(fields = {}, options = {})
 
           # set defaults
           FIELDS.each_key do |field|
-            instance_variable_set("@#{field}", FIELDS[field].default)
+            instance_variable_set(:"@#{field}", FIELDS[field].default)
           end
 
           # set given
           fields.each_key do |field|
-            instance_variable_set("@#{field}", fields[field])
+            instance_variable_set(:"@#{field}", fields[field])
           end
         end
 
@@ -90,7 +90,7 @@ def generate
 
           stack = []
           FIELDS.each_key do |k|
-            var = instance_variable_get("@#{k}")
+            var = instance_variable_get(:"@#{k}")
 
             # TODO: fix possible wrong format if alt parameters (last one) is given
             next if FIELDS[k][:skippable] && var.nil?
@@ -105,9 +105,9 @@ def generate
 
         def process
           FIELDS.each_key do |k|
-            var = instance_variable_get("@#{k}")
+            var = instance_variable_get(:"@#{k}")
 
-            instance_variable_set("@#{k}", FIELDS[k][:format].call(var)) if FIELDS[k][:format].is_a?(Proc)
+            instance_variable_set(:"@#{k}", FIELDS[k][:format].call(var)) if FIELDS[k][:format].is_a?(Proc)
           end
         end
 
@@ -115,7 +115,7 @@ def validate
           FIELDS.each_key do |k|
             next unless FIELDS[k][:validation]
 
-            var = instance_variable_get("@#{k}")
+            var = instance_variable_get(:"@#{k}")
 
             call_validator(FIELDS[k][:validation], var)
           end
@@ -133,7 +133,7 @@ def call_validator(validator, value)
             validator.call(value)
             # :nocov:
           when Symbol
-            send("#{validator}_validator", value)
+            send(:"#{validator}_validator", value)
           end
         end
 
diff --git a/lib/prawn/swiss_qr_bill/specifications.rb b/lib/prawn/swiss_qr_bill/specifications.rb
index 6cdb4d8..b6537e5 100644
--- a/lib/prawn/swiss_qr_bill/specifications.rb
+++ b/lib/prawn/swiss_qr_bill/specifications.rb
@@ -19,10 +19,10 @@ class Specifications
         height: Spec.new(nil, ->(v) { from_mm(v) }),
         content_font_size: Spec.new,
         content_font_leading: Spec.new(0),
-        content_font_style: Spec.new(:normal, ->(v) { v.to_sym }),
+        content_font_style: Spec.new(:normal, lambda(&:to_sym)),
         label_font_size: Spec.new,
         label_font_leading: Spec.new(0),
-        label_font_style: Spec.new(:bold, ->(v) { v.to_sym })
+        label_font_style: Spec.new(:bold, lambda(&:to_sym))
       }.freeze
 
       def initialize
diff --git a/spec/features/compatibility_spec.rb b/spec/features/compatibility_spec.rb
index 3d3851e..c31bee1 100644
--- a/spec/features/compatibility_spec.rb
+++ b/spec/features/compatibility_spec.rb
@@ -8,7 +8,7 @@
 
   describe '#swiss_qr_bill' do
     context 'when one argument is given' do
-      it 'works' do
+      it 'works without arguments' do
         document.swiss_qr_bill(bill_full)
       end
     end
diff --git a/spec/features/pdf_generation_spec.rb b/spec/features/pdf_generation_spec.rb
index ffeb60e..61df30a 100644
--- a/spec/features/pdf_generation_spec.rb
+++ b/spec/features/pdf_generation_spec.rb
@@ -11,7 +11,7 @@
   end
 
   before do
-    FileUtils.rm(outfile) if File.exist?(outfile)
+    FileUtils.rm_f(outfile)
   end
 
   after do |spec|
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 928585e..0b73469 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -30,4 +30,4 @@
 Dir["#{File.dirname(__FILE__)}/support/**/*.rb"].sort.each { |f| require f }
 
 # Ensure tmp dir
-FileUtils.mkdir(TMP_DIR) unless Dir.exist?(TMP_DIR)
+FileUtils.mkdir_p(TMP_DIR)