Add WaitForAndClearExpectations() for testing async side effects

[calder]

Would it be reasonable to add the following helper to gmock-spec-builders for testing functions with asynchronous side effects?

bool Mock::WaitForAndClearExpectations(void* mock_obj, std::chrono::nanoseconds timeout);

[gennadiycivil]

@calder Thank you for this proposal. Could you please provide more details, potential use case, and most importantly how are you accomplishing this "today"? Thanks again

[calder]

@gennadiycivil: Thanks! Here's an example use case:

Let's say we want to test the behavior of Foo::DoSomething().

• Foo takes a Bar in its constructor.
• Foo::DoSomething() calls Bar::DoSomethingElse() asynchronously (via std::async for example).

If Bar::DoSomethingElse() were called synchronously, we would just create a mock Bar, pass it to Foo's constructor, set up expectations on the Bar mock, and call Foo::DoSomething().

Instead, because it's asynchronous, after calling Foo::DoSomething() we have to either:

• Sleep long enough for Bar::DoSomethingElse() to probably have been called. This is undesirable because it slows down tests significantly, makes them brittle to timing changes, and introduces potential flakes.
• Modify production code to signal some synchronization primitive when the async operation completes. This is even less desirable since it impairs readability of production code.
• Set up a side effect on every mock method we want to wait for to signal a Notification when they have been correctly called. This adds a lot of boilerplate and hurts test readability.

So far I have usually opted for "sleep synchronization" with all its associated problems.

[calder]

@gennadiycivil: Does https://github.com/abseil/googletest/pull/1991 look like roughly the right direction?

[leunMar]

@calder @gennadiycivil This would be a very useful feature for testing in ROS, where we have asynchronous callbacks (http://wiki.ros.org/roscpp/Overview/Publishers%20and%20Subscribers).

Actually, there is another workaround: You can wake up a sleeping thread when the mock function is called defining an appropriate action. https://github.com/PilzDE/pilz_robots/blob/5a969f06e6b7626e2ddb3c485f0a5ca645bbaff4/prbt_hardware_support/test/include/prbt_hardware_support/async_test.h

[gennadiycivil]

See #1991