diff --git a/lib/slither.rb b/lib/slither.rb
index d3ab090..92aaace 100644
--- a/lib/slither.rb
+++ b/lib/slither.rb
@@ -1,16 +1,14 @@
 # frozen_string_literal: true
 
-require_relative 'slither/column'
-require_relative 'slither/definition'
-require_relative 'slither/generator'
-require_relative 'slither/parser'
-require_relative 'slither/section'
+require_relative "slither/column"
+require_relative "slither/definition"
+require_relative "slither/generator"
+require_relative "slither/parser"
+require_relative "slither/section"
 require_relative "slither/version"
 
 module Slither
   class Error < StandardError; end
-  # Your code goes here...
-
   class DuplicateColumnNameError < StandardError; end
   class RequiredSectionNotFoundError < StandardError; end
   class RequiredSectionEmptyError < StandardError; end
@@ -19,7 +17,13 @@ class ColumnMismatchError < StandardError; end
   class LineWrongSizeError < StandardError; end
   class SectionsNotSameLengthError < StandardError; end
 
-
+  # Define a Slither's definition to parse a file.
+  #
+  # name - String name of the definition, this should be unique.
+  # options - Hash of options to pass to the definition.
+  #           Ex: by_bytes: true, to parse by bytes
+  #           Ex: align: :left, to align the columns to the left
+  # block - Block to define the sections of the definition. See README.md for more info.
   def self.define(name, options = {}, &block)
     definition = Definition.new(options)
     yield(definition)
@@ -31,13 +35,14 @@ def self.define(name, options = {}, &block)
   def self.generate(definition_name, data)
     definition = definition(definition_name)
     raise ArgumentError, "Definition name '#{name}' was not found." unless definition
+
     generator = Generator.new(definition)
     generator.generate(data)
   end
 
   # Writes the File
   def self.write(filename, definition_name, data)
-    File.open(filename, 'w') do |f|
+    File.open(filename, "w") do |f|
       f.write generate(definition_name, data)
     end
   end
@@ -52,6 +57,7 @@ def self.parse(filename, definition_name)
   def self.parseIo(io, definition_name)
     definition = definition(definition_name)
     raise ArgumentError, "Definition name '#{definition_name}' was not found." unless definition
+
     parser = Parser.new(definition, io)
     definition.options[:by_bytes] ? parser.parse_by_bytes : parser.parse
   end
diff --git a/spec/slither_spec.rb b/spec/slither_spec.rb
index 3d82d8a..b50850f 100644
--- a/spec/slither_spec.rb
+++ b/spec/slither_spec.rb
@@ -8,38 +8,35 @@
 
   describe ".define" do
     it "creates a new definition using the specified name and options" do
-      definition = double("definition")
-
-      expect(subject).to receive(:define).with(name, options).and_return(definition)
-
-      subject.define(name, options)
-    end
-
-    it "pass the definition to the block" do
-      yielded = nil
-
-      described_class.define(name) do |y|
-        yielded = y
+      subject.define(name, options) do
+        # Empty block
       end
 
-      expect(yielded).to be_a(Slither::Definition)
+      definition = subject.send(:definitions)[name]
+
+      expect(definition).to be_a(Slither::Definition)
+      expect(definition.options).to eq(options.merge(by_bytes: true))
     end
 
     it "adds the definition to the internal definition count" do
       expect do
-        subject.define("new_definition", options) {}
+        # NOTE: as @@definitions is a class variable that's shared across the specs,
+        #       so we need to ensure we add a new one.
+        subject.define("#{name}-1", options) do
+          # Empty block
+        end
       end.to change { subject.send(:definitions).count }.by(1)
     end
   end
 
   describe ".generate" do
-    it "should raise an error if the definition name is not found" do
+    it "raise an error if the definition name is not found" do
       expect do
         subject.generate(:not_found_definition, {})
       end.to raise_error(ArgumentError)
     end
 
-    it "should output a string" do
+    it "output a string" do
       simple_definition
 
       expect(
@@ -54,7 +51,8 @@
     it "write a file" do
       simple_definition
 
-      file = double("file")
+      file = instance_double(File, "file")
+
       allow(File).to receive(:open).with(file_name, "w").and_yield(file)
       expect(file).to receive(:write)
 
@@ -89,7 +87,7 @@
           simple_definition
 
           expect(
-            Slither.parse(simple_definition_file, :simple)
+            subject.parse(simple_definition_file, :simple)
           ).to eq(simple_definition_test_data)
         end
       end