[dev.fuzz] testing: make F.Fuzz more similar to T.Run
This change rewrites much of the glue code in testing/fuzz.go to work
more analogously to T.Run. This results in improved behavior:
* If a fuzz target returns without calling F.Skip, F.Fail, or F.Fuzz,
'go test' will report an error and exit non-zero.
* Functions registered with F.Cleanup are called.
* The user can re-run individual inputs using -run=FuzzTarget/name
where name is the base name of the seed corpus file. We now print
the 'go test' command after a crash.
This change doesn't correctly handle T.Parallel calls yet, but it
should be easier to do that in the future.
Highlighted parts of this change:
* Instead of creating one F for all targets, create an F for each
target. F (actually common) holds the status, output, and cleanup
function list for each target, so it's important to keep them
separate.
* Run each target in its own goroutine via fRunner. fRunner is
analogous to tRunner. It runs cleanups and catches inappropriate
Goexits and panics.
* Run each input in its own goroutine via T.Run. This enables subtest
filtering with -test.run and ensures functions registered with
T.Cleanup (not F.Cleanup) are run at the appropriate time.
Change-Id: Iab1da14ead8bcb57746f8a76f4aebc625baa5792
Reviewed-on: https://go-review.googlesource.com/c/go/+/290693 Reviewed-by: Katie Hockman <katie@golang.org>
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>