Ruby Sep 23rd, 2014

How to use Mock and Stub in Minitest and Rspec?

Referenced in Minimalicious testing in Ruby 1.9 with MiniTest

  • A stub object is a pretend object that implement some of the interface of the object it pretends to be and returns predefined responses.
  • A mock object is similair to a stub but has another use case: it helps decide if the test case it is used in passes by verifying if it’s methods has been called or not.

Minitest::Mock

require 'minitest/mock'

stub

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[2] pry(main)> foo = Minitest::Mock.new
=> #<Minitest::Mock:0x82ff7b5c>
[3] pry(main)> foo.expect(:hi, 'hello')
=> #<Minitest::Mock:0x82ff7b5c>
[4] pry(main)> foo.hi
=> "hello"

mock

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[5] pry(main)> bar = Minitest::Mock.new
=> #<Minitest::Mock:0x821763e4>
[6] pry(main)> bar.expect(:hi, 'hello', ['arg1', 'arg2'])
=> #<Minitest::Mock:0x821763e4>
[7] pry(main)> bar.verify
MockExpectationError: expected hi("arg1", "arg2") => "hello", got []
[8] pry(main)> bar.hi('arg1', 'arg2')
=> "hello"
[9] pry(main)> bar.verify
=> true

RSpec::Mocks

require 'rspec/mocks/standalone'

stub

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[2] pry(main)> foo = double()
=> #<RSpec::Mocks::Mock:0x82c66b78 @name=nil>
[3] pry(main)> foo.stub(:hi).and_return('hello')
=> nil
[4] pry(main)> foo.hi
=> "hello"
[7] pry(main)> foo.stub(:hi).with('world').and_return('hello world')
=> nil
[9] pry(main)> foo.hi('world')
=> "hello world"

mock

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[18] pry(main)> foo = double()
=> #<RSpec::Mocks::Mock:0x82c66b78 @name=nil>
[19] pry(main)> foo.should_receive(:hi).with('world')
=> #<RSpec::Mocks::MessageExpectation:0x818c11f4>

Reference