Indicate when matcher logic is defined by block

Previously the output from a test where such an exception was not
matched was a bit confusing, because no expected parameters were
displayed. While we can't easily display the logic from the block
itself, we can at least highlight that such logic does exist.

While this will change the content of some test failure messages, I have
previously specified that is not part of the documented API. [1]

[1]: #577

lib/mocha/parameters_matcher.rb

@@ -22,9 +22,13 @@ def parameters_match?(actual_parameters)
     end
 
     def mocha_inspect
-      signature = matchers.mocha_inspect
-      signature = signature.gsub(/^\[|\]$/, '')
-      "(#{signature})"
+      if @matching_block
+        '(arguments_accepted_by_custom_matching_block)'
+      else
+        signature = matchers.mocha_inspect
+        signature = signature.gsub(/^\[|\]$/, '')
+        "(#{signature})"
+      end
     end
 
     def matchers

test/unit/parameters_matcher_test.rb

@@ -103,4 +103,9 @@ def test_should_indicate_that_matcher_will_match_any_actual_parameters
     parameters_matcher = ParametersMatcher.new
     assert_equal '(any_parameters)', parameters_matcher.mocha_inspect
   end
+
+  def test_should_indicate_that_matcher_logic_is_defined_by_custom_block
+    parameters_matcher = ParametersMatcher.new { true }
+    assert_equal '(arguments_accepted_by_custom_matching_block)', parameters_matcher.mocha_inspect
+  end
 end