Project: RSpec Expectations 3.7

Publisher: RSpec

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.

Scenarios

define a block matcher manually
define a block matcher using shortcut
define a block matcher using shortcut

define a block matcher manually

Given

a file named "block_matcher_spec.rb" with:

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

define a block matcher using shortcut

Given

a file named "block_matcher_spec.rb" with:

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

define a block matcher using shortcut

Given

a file named "block_matcher_spec.rb" with:

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 should support blocks with errors
     Failure/Error: expect(true).to eq false

       expected: false
            got: true

       (compared using ==)

Last published over 4 years ago by myronmarston.

define a matcher supporting block expectations

RSpec Expectations settings