The Mocha library is the one Rails uses for its own testing, so it seems the natural choice for a test-double library to use with Minitest. Full Mocha docs are available at

Installing Mocha

Mocha needs to be installed after Minitest, which requires a slight indirection to ensure your Rails app does the right thing.

First, in the Gemfile’s :test group, add the Mocha gem:

gem ​"mocha"​, require: false

The require: false ensures that Mocha loads in the correct order.

Then, inside the test/test_helper.rb file, you manually require Mocha at any point in the file after the rails/test_help library is loaded:

require ​"mocha/mini_test"

At that point we should be good to go. Please see Chapter 7, Using Test ...

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