define_diffable_matcher.feature

Feature: define diffable matcher

When a matcher is defined as diffable, and the --diff
flag is set, the output will include a diff of the submitted
objects.

Scenario: define a diffable matcher
  Given a file named "diffable_matcher_spec.rb" with:
    """
    Spec::Matchers.define :be_just_like do |expected|
      match do |actual|
        actual == expected
      end

      diffable
    end

    describe "this" do
      it {should be_just_like("that")}
    end
    """
  When I run "spec diffable_matcher_spec.rb --diff"
  Then the exit code should be 256

  And the stdout should include "should be just like \"that\""
  And the stdout should include "Diff:\n@@ -1,2 +1,2 @@\n-that\n+this"