diff --git a/.gitignore b/.gitignore
index c4901d00cae40b8b70dc6ce14b70deed097932fa..f0c7c3e4912696c342752e2ad7dc278b9830ec90 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 build/
+test/sandbox
 .DS_Store
 examples/example_1/test1.out
 examples/example_1/test2.out
diff --git a/auto/generate_module.rb b/auto/generate_module.rb
index 2ec14c57bdc76df7e4a1962ce508cb1b5e822a74..0fbaf559f80f0de50bff1d5185eec62be40d777f 100644
--- a/auto/generate_module.rb
+++ b/auto/generate_module.rb
@@ -187,14 +187,24 @@ class UnityModuleGenerator
 
     files = files_to_operate_on(module_name, pattern)
 
-    #Abort if any module already exists
+    #Abort if all of the module files already exist
+    all_files_exist = true
     files.each do |file|
-      raise "ERROR: File #{file[:name]} already exists. Exiting." if File.exist?(file[:path])
+      if not File.exist?(file[:path])
+        all_files_exist = false
+      end
     end
+    raise "ERROR: File #{files[0][:name]} already exists. Exiting." if all_files_exist
 
     # Create Source Modules
     files.each_with_index do |file, i|
-      FileUtils.mkdir_p(File.dirname(file[:path]), :verbose => false) # Create the path first if necessary.
+      # If this file already exists, don't overwrite it.
+      if File.exist?(file[:path])
+        puts "File #{file[:path]} already exists!"
+        next
+      end
+      # Create the path first if necessary.
+      FileUtils.mkdir_p(File.dirname(file[:path]), :verbose => false)
       File.open(file[:path], 'w') do |f|
         f.write("#{file[:boilerplate]}\n" % [file[:name]]) unless file[:boilerplate].nil?
         f.write(file[:template] % [ file[:name],
diff --git a/test/rakefile b/test/rakefile
index 5df66fbeeca6d34951cfd0e34655aaf568d191e7..000ab009a51568bcff1e911ae24b577b5c8a2944 100644
--- a/test/rakefile
+++ b/test/rakefile
@@ -10,9 +10,11 @@ $verbose = false
 require 'rake'
 require 'rake/clean'
 require UNITY_ROOT + 'rakefile_helper'
+require 'rspec/core/rake_task'
 
 TEMP_DIRS = [
-	File.join(UNITY_ROOT, 'build')
+	File.join(UNITY_ROOT, 'build'),
+	File.join(UNITY_ROOT, 'sandbox')
 ]
 
 TEMP_DIRS.each do |dir|
@@ -40,6 +42,11 @@ task :scripts => [:prepare_for_tests] do
   end
 end
 
+desc "Run all rspecs"
+RSpec::Core::RakeTask.new(:spec) do |t|
+  t.pattern = 'spec/**/*_spec.rb'
+end
+
 desc "Generate test summary"
 task :summary do
   report_summary
diff --git a/test/spec/generate_module_existing_file_spec.rb b/test/spec/generate_module_existing_file_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..74e7fc840284b4b75efb84dbe4c671bbaa4ea814
--- /dev/null
+++ b/test/spec/generate_module_existing_file_spec.rb
@@ -0,0 +1,158 @@
+
+require '../auto/generate_module.rb'
+require 'fileutils'
+
+def touch_src(file)
+  FileUtils.touch "sandbox/src/#{file}"
+end
+
+def touch_test(file)
+  FileUtils.touch "sandbox/test/#{file}"
+end
+
+def create_src_with_known_content(file)
+  File.open("sandbox/src/#{file}", "w") {|f| f.write("the original #{file}")}
+end
+
+def create_test_with_known_content(file)
+  File.open("sandbox/test/#{file}", "w") {|f| f.write("the original #{file}")}
+end
+
+def expect_src_content_didnt_change(file)
+  expect(File.read("sandbox/src/#{file}")).to eq("the original #{file}")
+end
+
+def expect_test_content_didnt_change(file)
+  expect(File.read("sandbox/test/#{file}")).to eq("the original #{file}")
+end
+
+def expect_src_file_to_exist(file)
+  expect(File.exist?("sandbox/src/#{file}")).to be true
+end
+
+def expect_test_file_to_exist(file)
+  expect(File.exist?("sandbox/test/#{file}")).to be true
+end
+
+describe "UnityModuleGenerator" do
+
+  before do
+    # clean sandbox and setup our "project" folders
+    FileUtils.rm_rf "sandbox"
+    FileUtils.mkdir_p "sandbox"
+    FileUtils.mkdir_p "sandbox/src"
+    FileUtils.mkdir_p "sandbox/test"
+
+    @options = {
+      :path_src => "sandbox/src",
+      :path_tst => "sandbox/test",
+    }
+  end
+
+  context "with src pattern" do
+    before do
+      @options[:pattern] = "src"
+    end
+
+    it "fails when all files already exist" do
+      # create an existing triad of files
+      touch_src "meh.c"
+      touch_src "meh.h"
+      touch_test "Testmeh.c"
+      expect {
+        UnityModuleGenerator.new(@options).generate("meh")
+      }.to raise_error("ERROR: File meh already exists. Exiting.")
+    end
+
+    it "creates the test file if the source and header files exist" do
+      # Create the existing files.
+      touch_src "meh.c"
+      touch_src "meh.h"
+
+      UnityModuleGenerator.new(@options).generate("meh")
+
+      expect_test_file_to_exist "Testmeh.c"
+    end
+
+    it "does not alter existing files" do
+      # Create some files with known content.
+      create_src_with_known_content "meh.c"
+      create_src_with_known_content "meh.h"
+
+      UnityModuleGenerator.new(@options).generate("meh")
+
+      expect_src_content_didnt_change "meh.c"
+      expect_src_content_didnt_change "meh.c"
+    end
+
+    it "does not alter existing test files" do
+      # Create some files with known content.
+      create_test_with_known_content "Testmeh.c"
+
+      UnityModuleGenerator.new(@options).generate("meh")
+
+      expect_test_content_didnt_change "Testmeh.c"
+    end
+
+  end
+
+  context "with mch pattern" do
+    before do
+      @options[:pattern] = "mch"
+    end
+
+    it "fails when all files exist" do
+        touch_src "meh_model.c"
+        touch_src "meh_conductor.c"
+        touch_src "meh_hardware.c"
+        touch_src "meh_model.h"
+        touch_src "meh_conductor.h"
+        touch_src "meh_hardware.h"
+        touch_test "Testmeh_model.c"
+        touch_test "Testmeh_conductor.c"
+        touch_test "Testmeh_hardware.c"
+        expect {
+          UnityModuleGenerator.new(@options).generate("meh")
+        }.to raise_error("ERROR: File meh_model already exists. Exiting.")
+    end
+
+    it "creates files that don't exist" do
+      touch_src "meh_model.c"
+      touch_src "meh_conductor.c"
+      touch_src "meh_hardware.c"
+      touch_src "meh_model.h"
+      touch_src "meh_conductor.h"
+
+      UnityModuleGenerator.new(@options).generate("meh")
+
+      expect_src_file_to_exist "meh_hardware.h"
+      expect_test_file_to_exist "Testmeh_model.c"
+      expect_test_file_to_exist "Testmeh_conductor.c"
+      expect_test_file_to_exist "Testmeh_hardware.c"
+    end
+
+    it "does not alter existing source files" do
+      create_src_with_known_content "meh_model.c"
+      create_src_with_known_content "meh_model.c"
+      create_src_with_known_content "meh_model.c"
+      create_src_with_known_content "meh_model.h"
+      create_src_with_known_content "meh_model.c"
+
+      UnityModuleGenerator.new(@options).generate("meh")
+
+      expect_src_content_didnt_change "meh_model.c"
+      expect_src_content_didnt_change "meh_model.c"
+      expect_src_content_didnt_change "meh_model.c"
+      expect_src_content_didnt_change "meh_model.c"
+    end
+
+    it "does not alter existing test files" do
+      create_test_with_known_content "Testmeh_model.c"
+
+      UnityModuleGenerator.new(@options).generate("meh")
+
+      expect_test_content_didnt_change "Testmeh_model.c"
+    end
+
+  end
+end