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Defining a matcher with fluent interface

Use the chain method to define matchers with a fluent interface.

Chained method with argument​

Given a file named "between_spec.rb" with:

RSpec::Matchers.define :be_bigger_than do |first|
  match do |actual|
    (actual > first) && (actual < @second)
  end

  chain :and_smaller_than do |second|
    @second = second
  end
end

RSpec.describe 5 do
  it { is_expected.to be_bigger_than(4).and_smaller_than(6) }
end

When I run rspec between_spec.rb --format documentation

Then the output should contain "1 example, 0 failures"

And the output should contain "is expected to be bigger than 4".

Chained setter​

Given a file named "between_spec.rb" with:

RSpec::Matchers.define :be_bigger_than do |first|
  match do |actual|
    (actual > first) && (actual < second)
  end

  chain :and_smaller_than, :second
end

RSpec.describe 5 do
  it { is_expected.to be_bigger_than(4).and_smaller_than(6) }
end

When I run rspec between_spec.rb --format documentation

Then the output should contain "1 example, 0 failures"

And the output should contain "is expected to be bigger than 4".

With include_chain_clauses_in_custom_matcher_descriptions configured to true, and chained method with argument​

Given a file named "between_spec.rb" with:

RSpec.configure do |config|
  config.expect_with :rspec do |c|
    c.include_chain_clauses_in_custom_matcher_descriptions = true
  end
end

RSpec::Matchers.define :be_bigger_than do |first|
  match do |actual|
    (actual > first) && (actual < @second)
  end

  chain :and_smaller_than do |second|
    @second = second
  end
end

RSpec.describe 5 do
  it { is_expected.to be_bigger_than(4).and_smaller_than(6) }
end

When I run rspec between_spec.rb --format documentation

Then the output should contain "1 example, 0 failures"

And the output should contain "is expected to be bigger than 4 and smaller than 6".