rslota / ex_assert_eventually Goto Github PK

Hello,

I'm curious if it's intentional behaviour that condition check inside eventually triggered at least twice even if the first call of it yields a successful result?

To demonstrate this I tweaked one of your tests:

    test "when match is successful from the first try" do
      {:ok, mock} =
        start_supervised(
          {MockOperation, [success_return: :ok, failure_return: :error, fail_times: 0]}
        )

      returne_value = assert_eventually :ok = MockOperation.do_something(mock), :ok

      assert returne_value == :ok

      stats = MockOperation.get_stats(mock)
      # by default there should be one call each 20ms
      assert stats.call_counter ==  1
    end

This test will fail as call_counter is gonna be equal 2 and not 1 even though the condition was met after the first call of eventually "block".

I looked through the tests and my guess is that you might have thought of scenarios when the state eventually settles and the assertion yields the same results from one point onward. But imagine the scenario when you getting messages from the queue and you are not sure whether the message is ready to be consumed or delay is required. assert_eventually looks like the right tool for this job, right? Wrong! If it's just one message and it's ready to be consumed by the time of the first call, it's gonna fetch it with the first call and will fail ugly later on even though the condition of assertion was met. This behaviour is unexpected and it took me some time to figure why my test fails as the matcher basically breaks the expectation of how it should behave.

Would it be possible to change that so assert_eventually would be useful in the scenario I described as well?

Consider this test:

   test "hello world" do
    eventually assert variable = Module.hello()
    assert :world == variable
  end

If you compile this on Elixir 1.11+ you get this warning:

Compiling 1 file (.ex)
Generated eventually_variable app
warning: variable "variable" is unused (if the variable is not meant to be used, prefix it with an underscore)
  test/eventually_variable_test.exs:8: EventuallyVariableTest."test get meaningful value by using normal assert"/1

..

Finished in 0.05 seconds
1 doctest, 1 test, 0 failures

Randomized with seed 920761

Obviously the variable is used later in the assert, but the compiler doesn't see that.