Minitest `must_call`

must_call.rb

# Wrapper to mock.verify procedure when asserting
# a method is called in minitest

class Object

  def must_call(method_name, returns: nil, arguments: [])
    mock = Minitest::Mock.new
    mock.expect(:call, returns, arguments)

    self.stub(method_name, mock) do
      yield
    end

    begin
      mock.verify.must_equal true
    rescue MockExpectationError
      # We want a better message than 'expected call() => nil'
      raise MockExpectationError,
        "Expected #{self.inspect} to call #{method_name}(#{arguments.inspect}) => #{returns.inspect}"
    end
  end

end