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Project: RSpec Expectations 3.1

Publisher: RSpec

`respond_to` matcher

Use the respond_to matcher to specify details of an object's interface. In its most basic form:

  expect(obj).to respond_to(:foo) # pass if obj.respond_to?(:foo)

You can specify that an object responds to multiple messages in a single statement with
multiple arguments passed to the matcher:

  expect(obj).to respond_to(:foo, :bar) # passes if obj.respond_to?(:foo) && obj.respond_to?(:bar)

If the number of arguments accepted by the method is important to you, you can specify
that as well:

  expect(obj).to respond_to(:foo).with(1).argument
  expect(obj).to respond_to(:bar).with(2).arguments

Note that this matcher relies entirely upon #respond_to?. If an object dynamically responds
to a message via #method_missing, but does not indicate this via #respond_to?, then this
matcher will give you false results.

Scenarios
basic usage
Given
a file named "respond_to_matcher_spec.rb" with: 
RSpec.describe "a string" do
  it { is_expected.to respond_to(:length) }
  it { is_expected.to respond_to(:hash, :class, :to_s) }
  it { is_expected.not_to respond_to(:to_model) }
  it { is_expected.not_to respond_to(:compact, :flatten) }

  # deliberate failures
  it { is_expected.to respond_to(:to_model) }
  it { is_expected.to respond_to(:compact, :flatten) }
  it { is_expected.not_to respond_to(:length) }
  it { is_expected.not_to respond_to(:hash, :class, :to_s) }

  # mixed examples--String responds to :length but not :flatten
  # both specs should fail
  it { is_expected.to respond_to(:length, :flatten) }
  it { is_expected.not_to respond_to(:length, :flatten) }
end
When
I run rspec respond_to_matcher_spec.rb
Then
the output should contain all of these:
10 examples, 6 failures
expected "a string" to respond to :to_model
expected "a string" to respond to :compact, :flatten
expected "a string" not to respond to :length
expected "a string" not to respond to :hash, :class, :to_s
expected "a string" to respond to :flatten
expected "a string" not to respond to :length
specify arguments
Given
a file named "respond_to_matcher_argument_checking_spec.rb" with: 
RSpec.describe 7 do
  it { is_expected.to respond_to(:zero?).with(0).arguments }
  it { is_expected.not_to respond_to(:zero?).with(1).argument }

  it { is_expected.to respond_to(:between?).with(2).arguments }
  it { is_expected.not_to respond_to(:between?).with(7).arguments }

  # deliberate failures
  it { is_expected.to respond_to(:zero?).with(1).argument }
  it { is_expected.not_to respond_to(:zero?).with(0).arguments }

  it { is_expected.to respond_to(:between?).with(7).arguments }
  it { is_expected.not_to respond_to(:between?).with(2).arguments }
end
When
I run rspec respond_to_matcher_argument_checking_spec.rb
Then
the output should contain all of these:
8 examples, 4 failures
expected 7 to respond to :zero? with 1 argument
expected 7 not to respond to :zero? with 0 arguments
expected 7 to respond to :between? with 7 arguments
expected 7 not to respond to :between? with 2 arguments

Last published about 6 years ago by myronmarston.