Minitest::AssertChanges

Introduces assert_changes and assert_no_changes to Minitest.

Add this line to your application's Gemfile:

gem 'minitest-assert_changes'

And then execute:

$ bundle

assert_changes is a more general assert_difference that works with any value.

assert_changes 'Error.current', from: nil, to: 'ERR' do
  expected_bad_operation
end

Can be called with strings, to be evaluated in the binding (context) of the block given to the assertion, or a lambda.

assert_changes -> { Error.current }, from: nil, to: 'ERR' do
  expected_bad_operation
end

The from and to arguments are compared with the case operator (===).

assert_changes 'Error.current', from: nil, to: Error do
  expected_bad_operation
end

This is pretty useful, if you need to loosely compare a value. For example, you need to test a token has been generated and it has that many random characters.

user = User.start_registration
assert_changes 'user.token', to: /\w{32}/ do
  user.finish_registration
end

The gem is available as open source under the terms of the MIT License.