Feature: define a matcher supporting block expectations

  When you wish to support block expectations (e.g. `expect { ... }.to matcher`) with
  your custom matchers you must specify this. You can do this manually (or determinately
  based on some logic) by defining a `supports_block_expectation?` method or by using
  the DSL's `supports_block_expectations` shortcut method.

  Scenario: define a block matcher manually
    Given a file named "block_matcher_spec.rb" with:
      """ruby
      RSpec::Matchers.define :support_blocks do
        match do |actual|
          actual.is_a? Proc
        end

        def supports_block_expectations?
          true # or some logic
        end
      end

      RSpec.describe "a custom block matcher" do
        specify { expect { }.to support_blocks }
      end
      """
    When I run `rspec ./block_matcher_spec.rb`
    Then the example should pass

  Scenario: define a block matcher using shortcut
    Given a file named "block_matcher_spec.rb" with:
      """ruby
      RSpec::Matchers.define :support_blocks do
        match do |actual|
          actual.is_a? Proc
        end

        supports_block_expectations
      end

      RSpec.describe "a custom block matcher" do
        specify { expect { }.to support_blocks }
      end
      """
    When I run `rspec ./block_matcher_spec.rb`
    Then the example should pass

  Scenario: define a block matcher using shortcut
    Given a file named "block_matcher_spec.rb" with:
      """ruby
      RSpec::Matchers.define :support_blocks_with_errors do
        match(:notify_expectation_failures => true) do |actual|
          actual.call
          true
        end

        supports_block_expectations
      end

      RSpec.describe "a custom block matcher" do
        specify do
          expect {
            expect(true).to eq false
          }.to support_blocks_with_errors
        end
      end
      """
    When I run `rspec ./block_matcher_spec.rb`
    Then it should fail with:
      """
      Failures:

        1) a custom block matcher is expected to support blocks with errors
           Failure/Error: expect(true).to eq false

             expected: false
                  got: true

             (compared using ==)
      """