Provide a helpful message if the diff between two objects is empty. F…

…ixes rspec#123

Changelog.md

@@ -1,3 +1,10 @@
+### dev
+[full changelog](http://github.com/rspec/rspec-expectations/compare/v2.9.0...master)
+
+Bug fixes
+
+* Provide a helpful message if the diff between two objects is empty.
+
 ### 2.9.0 / 2012-03-17
 [full changelog](http://github.com/rspec/rspec-expectations/compare/v2.8.0...v2.9.0)
 

lib/rspec/expectations/differ.rb

@@ -5,15 +5,12 @@
 module RSpec
   module Expectations
     class Differ
-      def initialize(ignore=nil)
-      end
-
       # This is snagged from diff/lcs/ldiff.rb (which is a commandline tool)
       def diff_as_string(data_new, data_old)
         data_old = data_old.split(/\n/).map! { |e| e.chomp }
         data_new = data_new.split(/\n/).map! { |e| e.chomp }
-        output = ""
         diffs = Diff::LCS.diff(data_old, data_new)
+        output = ""
         return output if diffs.empty?
         oldhunk = hunk = nil
         file_length_difference = 0
@@ -41,10 +38,18 @@ def diff_as_string(data_new, data_old)
         output << oldhunk.diff(format) << "\n"
       end
 
-      def diff_as_object(actual,expected)
-        actual = object_to_string(actual)
-        expected = object_to_string(expected)
-        diff_as_string(actual, expected)
+      def diff_as_object(actual, expected)
+        actual_as_string = object_to_string(actual)
+        expected_as_string = object_to_string(expected)
+        diff = diff_as_string(actual_as_string, expected_as_string)
+
+        if diff.empty?
+          "#{actual}.==(#{expected}) returned false even though the diff " \
+          "between #{actual} and #{expected} is empty. Check the " \
+          "implementation of #{actual}.==."
+        else
+          diff
+        end
       end
 
     protected

spec/rspec/expectations/differ_spec.rb

@@ -2,34 +2,15 @@
 require 'ostruct'
 
 module RSpec
-  module Fixtures
-    class Animal
-      def initialize(name,species)
-        @name,@species = name,species
-      end
+  module Expectations
+    describe Differ do
+      let(:differ) { RSpec::Expectations::Differ.new }
 
-      def inspect
-        <<-EOA
-<Animal
-  name=#{@name},
-  species=#{@species}
->
-        EOA
-      end
-    end
-  end
-end
-
-describe "Diff" do
-  before(:each) do
-    @options = OpenStruct.new(:diff_format => :unified, :context_lines => 3)
-    @differ = RSpec::Expectations::Differ.new(@options)
-  end
-
-  it "outputs unified diff of two strings" do
-    expected="foo\nbar\nzap\nthis\nis\nsoo\nvery\nvery\nequal\ninsert\na\nline\n"
-    actual="foo\nzap\nbar\nthis\nis\nsoo\nvery\nvery\nequal\ninsert\na\nanother\nline\n"
-    expected_diff= <<'EOD'
+      describe '#diff_as_string' do
+        it "outputs unified diff of two strings" do
+          expected="foo\nbar\nzap\nthis\nis\nsoo\nvery\nvery\nequal\ninsert\na\nline\n"
+          actual="foo\nzap\nbar\nthis\nis\nsoo\nvery\nvery\nequal\ninsert\na\nanother\nline\n"
+          expected_diff= <<'EOD'
 
 
 @@ -1,6 +1,6 @@
@@ -48,15 +29,58 @@ def inspect
  line
 EOD
 
-    diff = @differ.diff_as_string(expected, actual)
-    diff.should eql(expected_diff)
-  end
+          diff = differ.diff_as_string(expected, actual)
+          diff.should eql(expected_diff)
+        end
+      end
+
+      describe '#diff_as_object' do
+        it "outputs unified diff message of two objects" do
+          animal_class = Class.new do
+            def initialize(name, species)
+              @name, @species = name, species
+            end
 
-  it "outputs unified diff message of two arrays" do
-    expected = [ :foo, 'bar', :baz, 'quux', :metasyntactic, 'variable', :delta, 'charlie', :width, 'quite wide' ]
-    actual   = [ :foo, 'bar', :baz, 'quux', :metasyntactic, 'variable', :delta, 'tango'  , :width, 'very wide'  ]
+            def inspect
+              <<-EOA
+<Animal
+  name=#{@name},
+  species=#{@species}
+>
+              EOA
+            end
+          end
 
-    expected_diff = <<EOD
+          expected = animal_class.new "bob", "giraffe"
+          actual   = animal_class.new "bob", "tortoise"
+
+          expected_diff = <<'EOD'
+
+@@ -1,5 +1,5 @@
+ <Animal
+   name=bob,
+-  species=tortoise
++  species=giraffe
+ >
+EOD
+
+          diff = differ.diff_as_object(expected,actual)
+          diff.should == expected_diff
+        end
+
+        it "outputs a message if the diff is empty" do
+          diff = differ.diff_as_object('foo', 'foo')
+          diff.should eq(
+            "foo.==(foo) returned false even though the diff between " \
+            "foo and foo is empty. Check the implementation of foo.==."
+          )
+        end
+
+        it "outputs unified diff message of two arrays" do
+          expected = [ :foo, 'bar', :baz, 'quux', :metasyntactic, 'variable', :delta, 'charlie', :width, 'quite wide' ]
+          actual   = [ :foo, 'bar', :baz, 'quux', :metasyntactic, 'variable', :delta, 'tango'  , :width, 'very wide'  ]
+
+          expected_diff = <<'EOD'
 
 
 @@ -5,7 +5,7 @@
@@ -70,33 +94,15 @@ def inspect
 + "quite wide"]
 EOD
 
-    diff = @differ.diff_as_object(expected,actual)
-    diff.should == expected_diff
-  end
-
-  it "outputs unified diff message of two objects" do
-    expected = RSpec::Fixtures::Animal.new "bob", "giraffe"
-    actual   = RSpec::Fixtures::Animal.new "bob", "tortoise"
-
-    expected_diff = <<'EOD'
-
-@@ -1,5 +1,5 @@
- <Animal
-   name=bob,
--  species=tortoise
-+  species=giraffe
- >
-EOD
-
-    diff = @differ.diff_as_object(expected,actual)
-    diff.should == expected_diff
-  end
+          diff = differ.diff_as_object(expected,actual)
+          diff.should == expected_diff
+        end
 
-  it "outputs unified diff message of two hashes" do
-    expected = { :foo => 'bar', :baz => 'quux', :metasyntactic => 'variable', :delta => 'charlie', :width =>'quite wide' }
-    actual   = { :foo => 'bar', :metasyntactic => 'variable', :delta => 'charlotte', :width =>'quite wide' }
+        it "outputs unified diff message of two hashes" do
+          expected = { :foo => 'bar', :baz => 'quux', :metasyntactic => 'variable', :delta => 'charlie', :width =>'quite wide' }
+          actual   = { :foo => 'bar', :metasyntactic => 'variable', :delta => 'charlotte', :width =>'quite wide' }
 
-    expected_diff = <<'EOD'
+          expected_diff = <<'EOD'
 
 @@ -1,4 +1,5 @@
 -:delta => "charlotte",
@@ -107,38 +113,41 @@ def inspect
  :width => "quite wide"
 EOD
 
-    diff = @differ.diff_as_object(expected,actual)
-    diff.should == expected_diff
-  end
+          diff = differ.diff_as_object(expected,actual)
+          diff.should == expected_diff
+        end
 
-  it "outputs unified diff of single line strings" do
-    expected = "this is one string"
-    actual   = "this is another string"
+        it "outputs unified diff of single line strings" do
+          expected = "this is one string"
+          actual   = "this is another string"
 
-    expected_diff = <<EOD
+          expected_diff = <<'EOD'
 
 @@ -1,2 +1,2 @@
 -"this is another string"
 +"this is one string"
 EOD
 
-    diff = @differ.diff_as_object(expected,actual)
-    diff.should == expected_diff
-  end
+          diff = differ.diff_as_object(expected,actual)
+          diff.should == expected_diff
+        end
 
-  it "outputs unified diff of multi line strings" do
-    expected = "this is:\n  one string"
-    actual   = "this is:\n  another string"
+        it "outputs unified diff of multi line strings" do
+          expected = "this is:\n  one string"
+          actual   = "this is:\n  another string"
 
-    expected_diff = <<EOD
+          expected_diff = <<'EOD'
 
 @@ -1,3 +1,3 @@
  this is:
 -  another string
 +  one string
 EOD
 
-    diff = @differ.diff_as_object(expected,actual)
-    diff.should == expected_diff
+          diff = differ.diff_as_object(expected,actual)
+          diff.should == expected_diff
+        end
+      end
+    end
   end
 end