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minitest/mock, by Steven Baker, is a beautifully tiny mock (and stub) object framework.

The minitest-mock gem is an extraction of minitest/mock.rb from minitest in order to make it easier to maintain independent of minitest.

• minitest/mock - a simple and clean mock/stub system.

• Written by squishy human beings. Software can never be perfect. We will all eventually die.

Mocks and stubs defined using terminology by Fowler & Meszaros at www.martinfowler.com/bliki/TestDouble.html:

“Mocks are pre-programmed with expectations which form a specification of the calls they are expected to receive. They can throw an exception if they receive a call they don’t expect and are checked during verification to ensure they got all the calls they were expecting.”

class MemeAsker
  def initialize(meme)
    @meme = meme
  end

  def ask(question)
    method = question.tr(" ", "_") + "?"
    @meme.__send__(method)
  end
end

require "minitest/autorun"

describe MemeAsker, :ask do
  describe "when passed an unpunctuated question" do
    it "should invoke the appropriate predicate method on the meme" do
      @meme = Minitest::Mock.new
      @meme_asker = MemeAsker.new @meme
      @meme.expect :will_it_blend?, :return_value

      @meme_asker.ask "will it blend"

      @meme.verify
    end
  end
end

Minitest mocks do not support multi-threading. If it works, fine, if it doesn’t you can use regular ruby patterns and facilities like local variables. Here’s an example of asserting that code inside a thread is run:

def test_called_inside_thread
  called = false
  pr = Proc.new { called = true }
  thread = Thread.new(&pr)
  thread.join
  assert called, "proc not called"
end

Mocks and stubs are defined using terminology by Fowler & Meszaros at www.martinfowler.com/bliki/TestDouble.html:

“Stubs provide canned answers to calls made during the test”.

Minitest’s stub method overrides a single method for the duration of the block.

def test_stale_eh
  obj_under_test = Something.new

  refute obj_under_test.stale?

  Time.stub :now, Time.at(0) do   # stub goes away once the block is done
    assert obj_under_test.stale?
  end
end

A note on stubbing: In order to stub a method, the method must actually exist prior to stubbing. Use a singleton method to create a new non-existing method:

def obj_under_test.fake_method
  ...
end

• Ruby 3.2+

gem install minitest-mock

or

bundle add minitest-mock

(The MIT License)

Copyright © Ryan Davis, seattle.rb

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.