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由 Genadi Samokovarov 提交于
Those are assertions that I really do miss from the standard `ActiveSupport::TestCase`. Think of those as a more general version of `assert_difference` and `assert_no_difference` (those can be implemented by assert_changes, should this change be accepted). Why do we need those? They are useful when you want to check a side-effect of an operation. `assert_difference` do cover a really common case, but we `assert_changes` gives us more control. Having a global error flag? You can test it easily with `assert_changes`. In fact, you can be really specific about the initial state and the terminal one. ```ruby error = Error.new(:bad) assert_changes -> { Error.current }, from: nil, to: error do expected_bad_operation end ``` `assert_changes` follows `assert_difference` and a string can be given for evaluation as well. ```ruby error = Error.new(:bad) assert_changes 'Error.current', from: nil, to: error do expected_bad_operation end ``` Check out the test cases if you wanna see more examples.
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