Needs tests, but would like comments. Launch visual diff tool for comparing registered stub bodies and attempted request

lib/webmock.rb

@@ -16,6 +16,7 @@
 require 'webmock/http_lib_adapters/typhoeus_hydra_adapter'
 
 require 'webmock/errors'
+require 'webmock/registered_stub_differ'
 
 require 'webmock/util/uri'
 require 'webmock/util/headers'

lib/webmock/errors.rb

@@ -1,7 +1,8 @@
 module WebMock
-
   class NetConnectNotAllowedError < StandardError
     def initialize(request_signature)
+      WebMock::RegisteredStubDiffer.new(request_signature.body) if ENV['show_visual_diffs_for_webmock']
+
       text = "Real HTTP connections are disabled. Unregistered request: #{request_signature}"
       text << "\n\n"
       text << stubbing_instructions(request_signature)
@@ -29,5 +30,4 @@ def stubbing_instructions(request_signature)
       text
     end
   end
-
 end

lib/webmock/registered_stub_differ.rb

@@ -0,0 +1,55 @@
+module WebMock
+  class RegisteredStubDiffer
+    def initialize body
+      if body
+        FileUtils.mkdir_p stub_directory
+
+        save_attempted_file body
+
+        registered = save_registered_stubs
+        registered.each { |r| diff r }
+
+        cleanup registered
+      end
+    end
+
+    private
+
+    def diff registered
+      `#{diff_tool} #{registered} #{attempted_file} &`
+    end
+
+    def attempted_file
+      File.join stub_directory, "attempted_stub.txt"
+    end
+
+    def stub_directory
+      File.join %w(tmp webmock)
+    end
+
+    def cleanup files
+      File.delete attempted_file, *files
+    end
+
+    def save_attempted_file body
+      File.open(attempted_file, "w") { |f| f << body }
+    end
+
+    def save_registered_stubs
+      WebMock::StubRegistry.instance.request_stubs.map.
+        each_with_index do |stub, index|
+        file = "tmp/webmock/registered_stub_#{index}"
+
+        File.open file, "w" do |f|
+          f << stub.request_pattern.body_pattern
+        end
+
+        file
+        end
+    end
+
+    def diff_tool
+      ENV['diff_tool'] || "opendiff"
+    end
+  end
+end

spec/unit/registered_stub_differ_spec.rb

@@ -0,0 +1,4 @@
+require File.expand_path('spec/spec_helper')
+
+describe WebMock::RegisteredStubDiffer do
+end