src/cmd/go/testdata/script/test_fuzz_mutator_repeat.txt

# TODO(jayconrod): support shared memory on more platforms.
[!GOOS:darwin] [!GOOS:linux] [!GOOS:windows] skip

# Verify that the fuzzing engine records the actual crashing input, even when
# a worker process terminates without communicating the crashing input back
# to the coordinator.

[short] skip
env GOCACHE=$WORK/cache

# Start fuzzing. The worker crashes after 100 iterations.
# The fuzz function writes the crashing input to "want" before exiting.
# The fuzzing engine reconstructs the crashing input and saves it to testdata.
! exists want
! go test -fuzz=. -parallel=1 -fuzztime=110x -fuzzminimizetime=10x -v
stdout '^\s+fuzzing process hung or terminated unexpectedly: exit status'
stdout 'Failing input written to testdata'

# Run the fuzz target without fuzzing. The fuzz function is called with the
# crashing input in testdata. The test passes if that input is identical to
# the one saved in "want".
exists want
go test -want=want

-- go.mod --
module fuzz

go 1.17
-- fuzz_test.go --
package fuzz

import (
	"bytes"
	"flag"
	"os"
	"testing"
)

var wantFlag = flag.String("want", "", "file containing previous crashing input")

func FuzzRepeat(f *testing.F) {
	i := 0
	f.Fuzz(func(t *testing.T, b []byte) {
		i++
		if i == 100 {
			f, err := os.OpenFile("want", os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0666)
			if err != nil {
				// Couldn't create the file. Return without crashing, and try
				// again.
				i--
				t.Skip(err)
			}
			if _, err := f.Write(b); err != nil {
				// We already created the file, so if we failed to write it
				// there's not much we can do. The test will fail anyway, but
				// at least make sure the error is logged to stdout.
				t.Fatal(err)
			}
			if err := f.Close(); err != nil {
				t.Fatal(err)
			}
			os.Exit(1) // crash without communicating
		}

		if *wantFlag != "" {
			want, err := os.ReadFile(*wantFlag)
			if err != nil {
				t.Fatal(err)
			}
			if !bytes.Equal(want, b) {
				t.Fatalf("inputs are not equal!\n got: %q\nwant:%q", b, want)
			}
		}
	})
}