Mocking in RSpec VS Minitest: A Cheatsheet

January 05, 2022

My first exposure to a testing library in Ruby and Rails was RSpec, but I’m now using Minitest. It wasn’t immediately obvious how to translate rspec-expectations and rspec-mocks to Minitest, so here’s my attempt at a cheatsheet:

RSpec	minitest with mocha	minitest with minitest/mocks
`double`	`mock` or `stub`	`Minitest::Mock.new`
`instance_double`	`stub` or `mock.responds_like_instance_of`	Not supported
`expect().to receive().with().and_return()`	`mock.expects().with().returns()` Note: like RSpec, can also call `expects` on any object, not just a `Mock`/`Stub` `with` has imprecise keyword arg matching in Ruby 3	`mock = Minitest::Mock.new` `mock.expect(:method, args, return)` `mock.verify` Note: cannot call `expect` on any Object, but can make a Mock delegate to an underlying object
`expect().not_to receive()`	`mock.expects().never`	Technically you could use `Object#stub` and raise in the `val_or_callable`
`expect()... and yield_control()`	`mock.expects().yields(*parameters)` See docs	Not supported since return value is not a callable
`expect()... and raise_error()`	`mock.expects().raises(error)` See docs	Can pass in a block (instead of expected args) to `expect` and raise there
`allow()...`	Similar as above but substitute `expects` with `stubs`	Can use `Object#stub`
`.and_call_original`	Not supported (see reasoning)	Not supported
`allow_any_instance_of.Klass`	`Klass.any_instance.stubs`	Not supported

It’s very possible I’ve gotten something wrong - please feel free to correct in the comments or submit a PR!

Footnotes

For the curious, I wrote about how minitest/mock works here

Overspecifying Tests - the Employee Report Kata

Reading a Ruby gem with VSCode

Practical Metaprogramming in Ruby: minitest/mock

How does ActiveRecord know the primary_key?

wasabigeek

Mocking in RSpec VS Minitest: A Cheatsheet

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