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Project: RSpec Expectations 3.12

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
  expect(obj).to respond_to(:baz).with(1..2).arguments
  expect(obj).to respond_to(:xyz).with_unlimited_arguments

If your Ruby version supports keyword arguments, you can specify a list of keywords accepted
by the method.

  expect(obj).to respond_to(:foo).with_keywords(:ichi, :ni)
  expect(obj).to respond_to(:bar).with(2).arguments.and_keywords(:san, :yon)
  expect(obj).to respond_to(:baz).with_arbitrary_keywords

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
  1. basic usage
  2. specify arguments
  3. specify arguments range
  4. specify unlimited arguments
  5. specify keywords
  6. specify any keywords
  7. specify required keywords
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
  • @skip-when-splat-args-unsupported
specify arguments range
Given
a file named "respond_to_matcher_argument_range_checking_spec.rb" with: 
class MyClass
  def build(name, options = {})
  end

  def inspect
    'my_object'
  end
end

RSpec.describe MyClass do
  it { is_expected.to respond_to(:build).with(1..2).arguments }
  it { is_expected.not_to respond_to(:build).with(0..1).arguments }
  it { is_expected.not_to respond_to(:build).with(2..3).arguments }
  it { is_expected.not_to respond_to(:build).with(0..3).arguments }

  # deliberate failures
  it { is_expected.not_to respond_to(:build).with(1..2).arguments }
  it { is_expected.to respond_to(:build).with(0..1).arguments }
  it { is_expected.to respond_to(:build).with(2..3).arguments }
  it { is_expected.to respond_to(:build).with(0..3).arguments }
end
When
I run rspec respond_to_matcher_argument_range_checking_spec.rb
Then
the output should contain all of these:
8 examples, 4 failures
expected my_object not to respond to :build with 1..2 arguments
expected my_object to respond to :build with 0..1 arguments
expected my_object to respond to :build with 2..3 arguments
expected my_object to respond to :build with 0..3 arguments
  • @skip-when-splat-args-unsupported
specify unlimited arguments
Given
a file named "respond_to_matcher_unlimited_argument_checking_spec.rb" with: 
class MyClass
  def greet(message = 'Hello', *people)
  end

  def hail(person)
  end

  def inspect
    'my_object'
  end
end

RSpec.describe MyClass do
  it { is_expected.to respond_to(:greet).with_unlimited_arguments }
  it { is_expected.to respond_to(:greet).with(1).argument.and_unlimited_arguments }
  it { is_expected.not_to respond_to(:hail).with_unlimited_arguments }
  it { is_expected.not_to respond_to(:hail).with(1).argument.and_unlimited_arguments }

  # deliberate failures
  it { is_expected.not_to respond_to(:greet).with_unlimited_arguments }
  it { is_expected.not_to respond_to(:greet).with(1).argument.and_unlimited_arguments }
  it { is_expected.to respond_to(:hail).with_unlimited_arguments }
  it { is_expected.to respond_to(:hail).with(1).argument.and_unlimited_arguments }
end
When
I run rspec respond_to_matcher_unlimited_argument_checking_spec.rb
Then
the output should contain all of these:
8 examples, 4 failures
expected my_object not to respond to :greet with unlimited arguments
expected my_object not to respond to :greet with 1 argument and unlimited arguments
expected my_object to respond to :hail with unlimited arguments
expected my_object to respond to :hail with 1 argument and unlimited arguments
  • @skip-when-keyword-args-unsupported
specify keywords
Given
a file named "respond_to_matcher_keyword_checking_spec.rb" with: 
class MyClass
  def find(name = 'id', limit: 1_000, offset: 0)
    []
  end

  def inspect
    'my_object'
  end
end

RSpec.describe MyClass do
  it { is_expected.to respond_to(:find).with_keywords(:limit, :offset) }
  it { is_expected.to respond_to(:find).with(1).argument.and_keywords(:limit, :offset) }

  it { is_expected.not_to respond_to(:find).with_keywords(:limit, :offset, :page) }
  it { is_expected.not_to respond_to(:find).with(1).argument.and_keywords(:limit, :offset, :page) }

  # deliberate failures
  it { is_expected.to respond_to(:find).with_keywords(:limit, :offset, :page) }
  it { is_expected.to respond_to(:find).with(1).argument.and_keywords(:limit, :offset, :page) }

  it { is_expected.not_to respond_to(:find).with_keywords(:limit, :offset) }
  it { is_expected.not_to respond_to(:find).with(1).argument.and_keywords(:limit, :offset) }
end
When
I run rspec respond_to_matcher_keyword_checking_spec.rb
Then
the output should contain all of these:
8 examples, 4 failures
expected my_object to respond to :find with keywords :limit, :offset, and :page
expected my_object to respond to :find with 1 argument and keywords :limit, :offset, and :page
expected my_object not to respond to :find with keywords :limit and :offset
expected my_object not to respond to :find with 1 argument and keywords :limit and :offset
  • @skip-when-keyword-args-unsupported
specify any keywords
Given
a file named "respond_to_matcher_any_keywords_checking_spec.rb" with: 
class MyClass
  def build(name: 'object', **opts)
  end

  def create(name: 'object', type: String)
  end

  def inspect
    'my_object'
  end
end

RSpec.describe MyClass do
  it { is_expected.to respond_to(:build).with_any_keywords }
  it { is_expected.to respond_to(:build).with_keywords(:name).and_any_keywords }
  it { is_expected.not_to respond_to(:create).with_any_keywords }
  it { is_expected.not_to respond_to(:create).with_keywords(:name).and_any_keywords }

  # deliberate failures
  it { is_expected.not_to respond_to(:build).with_any_keywords }
  it { is_expected.not_to respond_to(:build).with_keywords(:name).and_any_keywords }
  it { is_expected.to respond_to(:create).with_any_keywords }
  it { is_expected.to respond_to(:create).with_keywords(:name).and_any_keywords }
end
When
I run rspec respond_to_matcher_any_keywords_checking_spec.rb
Then
the output should contain all of these:
8 examples, 4 failures
expected my_object not to respond to :build with any keywords
expected my_object not to respond to :build with keyword :name and any keywords
expected my_object to respond to :create with any keywords
expected my_object to respond to :create with keyword :name and any keywords
  • @skip-when-required-keyword-args-unsupported
specify required keywords
Given
a file named "respond_to_matcher_required_keyword_checking_spec.rb" with: 
class MyClass
  def plant(seed:, fertilizer: nil, water: 'daily')
    []
  end

  def inspect
    'my_object'
  end
end

RSpec.describe MyClass do
  it { is_expected.to respond_to(:plant).with_keywords(:seed) }
  it { is_expected.to respond_to(:plant).with_keywords(:seed, :fertilizer, :water) }
  it { is_expected.not_to respond_to(:plant).with_keywords(:fertilizer, :water) }

  # deliberate failures
  it { is_expected.not_to respond_to(:plant).with_keywords(:seed) }
  it { is_expected.not_to respond_to(:plant).with_keywords(:seed, :fertilizer, :water) }
  it { is_expected.to respond_to(:plant).with_keywords(:fertilizer, :water) }
end
When
I run rspec respond_to_matcher_required_keyword_checking_spec.rb
Then
the output should contain all of these:
6 examples, 3 failures
expected my_object not to respond to :plant with keyword :seed
expected my_object not to respond to :plant with keywords :seed, :fertilizer, and :water
expected my_object to respond to :plant with keywords :fertilizer and :water

Last published 3 months ago by Jon Rowe.