Dear all, Recently I find quite often that after "go test -fuzz" reported an error, the command shown to re-run the test does not reproduce the failure. For example, just now I got the following:
voss@dumpling [..nt/tounicode2] go test -fuzz FuzzToUnicode fuzz: elapsed: 0s, gathering baseline coverage: 0/2 completed fuzz: elapsed: 0s, gathering baseline coverage: 2/2 completed, now fuzzing with 10 workers fuzz: elapsed: 3s, execs: 280461 (93481/sec), new interesting: 24 (total: 26) fuzz: elapsed: 5s, execs: 410320 (72348/sec), new interesting: 60 (total: 62) --- FAIL: FuzzToUnicode (4.80s) --- FAIL: FuzzToUnicode (0.00s) tounicode_test.go:129: template: tounicode:26:2: executing "tounicode" at <Single $cs .>: error calling Single: runtime error: integer divide by zero Failing input written to testdata/fuzz/FuzzToUnicode/2566873a28045c1b To re-run: go test -run=FuzzToUnicode/2566873a28045c1b FAIL exit status 1 FAIL seehuhn.de/go/pdf/font/tounicode2 4.957s voss@dumpling [..nt/tounicode2] go test -run=FuzzToUnicode/2566873a28045c1b PASS ok seehuhn.de/go/pdf/font/tounicode2 0.122s The fuzzer reported a failure, and when I re-run the test I get a "PASS". How to debug such a problem? I understand that my fuzz function may somehow be non-deterministic, but so far I have not found any cause of non-determinism and re-running the test 10 times gives me 10 passes. Also, for a bug the fuzzer reported earlier, I found it very hard to believe that the given input could make the fuzz function reach the site of the error message. Could it be that the fuzzer sometimes looses track of which input belongs to which fuzzing run, and then reports the wrong input? If somebody wants to play with this, here is how to reproduce (up to randomness) the fuzzing run shown above: git clone https://github.com/seehuhn/go-pdf.git cd go-pdf/ git reset --hard 26c235ad cd font/tounicode2/ go test -fuzz FuzzToUnicode Any suggestions on how to debug such errors would be most welcome. Many thanks, Jochen -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/3fe3725b-e59e-4b1f-a2e9-0f28c15ea3d4n%40googlegroups.com.