Minitest how to solve mocked method :call expects 0 arguments, got 1

Question

I have a service with the call method to stub. But its always have this error:

SomeTest#test_1:
ArgumentError: mocked method :call expects 0 arguments, got 1
    test.rb:17:in `block in test_1'
    test.rb:16:in `test_1'

Here's the code:

require 'minitest/autorun'

class SomeService
  def initialize(headers = {})
  end

  def call
  end
end

class SomeTest < Minitest::Test
  def test_1
    mock = Minitest::Mock.new
    mock.expect :call, nil

    SomeService.stub :new, mock do
      SomeService.new({}).call
    end
  end
end

What did I do wrong? thanks

Answer 1

In general what you wrote is right but you hit and edge case with the method name call.

As you can see in the documentation of stub method.

"If val_or_callable responds to #call, then it returns the result of calling it".

So basically the problem is your mock responds to call, and the stub method is calling it before entering the block. You can solve it by wrapping the mock in a lambda that discards the arguments.

require 'minitest/autorun'

class SomeService
  def initialize(headers = {})
  end

  def call
  end
end

class SomeTest < Minitest::Test
  def test_1
    mock = Minitest::Mock.new
    mock.expect :call, nil

    SomeService.stub :new, ->(_args) { mock } do
      SomeService.new({}).call
    end
  end
end