REJECT and ASSUME are useful for filtering out unwanted generated
values. While this is not ideal, it is ocassionally useful and so we
include it for convenience.
The main loop of RANDOMIZED_TEST_CASE runs the test case 100 times, each
time trying to generate a different set of values. Inside that loop, if
it sees a REJECT (ASSUME is implemented in terms of REJECT), it retries
up to 15 times before giving up (perhaps it's impossible or just very
improbable to generate a value that will survive REJECT or ASSUME).
REJECT("Reason for rejecting") will just outright fail, while
ASSUME(bool) is more of an equivalent of a .filter() method from
functional languages.
This will be a foundational part of bootstrapping generators: this is
the way they'll get prerecorded values from / record random values into
RandomRuns. (Generators don't get in contact with RandomRuns
themselves, they just interact with the RandomnessSource.)
This will be used in the randomized tests a lot more than it is in the
unit tests / benchmarks; randomized tests will run the test function
multiple times, check the result and optionally start shrinking the
failing input. Generators will also be able to fail, resulting in some
of the new TestResult variants.
