Can I get log output only for failures with boost unit tests

Question

I have some logging in my application (it happens to be log4cxx but I am flexible on that), and I have some unit tests using the boost unit test framework. When my unit tests run, I get lots of log output, from both the passing and failing tests (not just boost assertions logged, but my own application code's debug logging too). I would like to get the unit test framework to throw away logs during tests that pass, and output logs from tests that fail (I grew to appreciate this behaviour while using python/nose).

Is there some standard way of doing this with the boost unit test framework? If not, are there some start of test/end of test hooks that I could use to buffer my logs and conditionally output them to implement this behaviour myself?

Answer 1

There are start of test and end of test hooks that you can use for this purpose. To set up these hooks you need to define a subclass of boost::unit_test::test_observer, create an instance of the class that will persist throughout the entire test (either a static global object or a BOOST_TEST_GLOBAL_FIXTURE), and then pass the class to boost::unit_test::framework::register_observer.

The method to override with a start of test hook is test_unit_start, and the method to override with an end of test hook is test_unit_finish. However, these hooks fire both for test suites as well as individual test cases, which may be an issue depending on how the hooks are set up. The test_unit_finish hook also doesn't explicitly tell you whether a given test actually passed, and there doesn't seem to be one clear and obvious way to get that information. There is a boost::unit_test::results_collector singleton, which has a results() method, and if you pass it the test_unit_id of the test unit provided to test_unit_finish, you get a test_results object that has a passed() method. I can't really see a way to get the test_unit_id that is clearly part of the public API -- you can just directly access the p_id member, but that could always change in a future boost version. You could also manually track whether each test is passing or failing using the assertion_result, exception_caught, test_unit_aborted, and test_unit_timed_out hooks from the test_observer subclass (assertion_result indicates a failure of the current test whenever its argument is false and every other hook indicates a failure if it is called at all).

Answer 2

According to the Boost.Test documentation, run your test executable with --log_level=error. This will catch only failing test cases.

I checked that it works using a BOOST_CHECK(false) on an otherwise correctly running project with a few thousand unit tests.

Running with --log_level=all gives the result of all assertions. I checked that by piping it to wc -l that the number of lines in the log is exactly the same as the number of assertions in the tests (which number is also reported by --report_level=detailed). You could of course also grep the log for the strings error or failed.