Define fail_with_message_including matcher

spec/support/fail_with_message_including_matcher.rb

@@ -0,0 +1,33 @@
+RSpec::Matchers.define :fail_with_message_including do |expected|
+  match do |block|
+    @actual = nil
+
+    begin
+      block.call
+    rescue RSpec::Expectations::ExpectationNotMetError => ex
+      @actual = ex.message
+    end
+
+    @actual && @actual.include?(expected)
+  end
+
+  failure_message_for_should do
+    msg = "Expectation should have failed with message including '#{expected}'"
+
+    if @actual
+      msg << ", actually failed with '#{@actual}'"
+    else
+      msg << ", but did not fail."
+    end
+
+    msg
+  end
+
+  failure_message_for_should_not do
+    msg  = "Expectation should not have failed with message including '#{expected}'"
+    msg << ", but did."
+
+    msg
+  end
+
+end