[dev.fuzz] testing: adjust -fuzz multiple match stdout

Fixes golang/go#48131

Change-Id: I40ff130c849dffe38363ddc0282e93ceb74ae140
Reviewed-on: https://go-review.googlesource.com/c/go/+/349969
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

3 files changed, 15 insertions, 17 deletions

diff --git a/src/cmd/go/testdata/script/test_fuzz_match.txt b/src/cmd/go/testdata/script/test_fuzz_match.txt
index 9d4c5125d3..47e143952a 100644
--- a/src/cmd/go/testdata/script/test_fuzz_match.txt
+++ b/src/cmd/go/testdata/script/test_fuzz_match.txt
@@ -30,11 +30,10 @@ stdout '^ok.*no tests to run'
 ! stdout 'no targets to fuzz'
 
 # Matches more than one fuzz target for fuzzing.
-go test -fuzz Fuzz -fuzztime 1x multiple_fuzz_test.go
-# The tests should run, but not be fuzzed
+! go test -fuzz Fuzz -fuzztime 1x multiple_fuzz_test.go
 ! stdout 'no tests to run'
 ! stdout 'no targets to fuzz'
-stdout ok
+stdout FAIL
 stdout 'will not fuzz, -fuzz matches more than one target'
 
 -- standalone_fuzz_test.go --
diff --git a/src/testing/fuzz.go b/src/testing/fuzz.go
index 65c3437ed4..c2d9db843d 100644
--- a/src/testing/fuzz.go
+++ b/src/testing/fuzz.go
@@ -593,12 +593,12 @@ func runFuzzTargets(deps testDeps, fuzzTargets []InternalFuzzTarget, deadline ti
 //
 // If fuzzing is disabled (-test.fuzz is not set), runFuzzing
 // returns immediately.
-func runFuzzing(deps testDeps, fuzzTargets []InternalFuzzTarget) (ran bool, matched int, ok bool) {
+func runFuzzing(deps testDeps, fuzzTargets []InternalFuzzTarget) (ok bool) {
 	// TODO(katiehockman,jayconrod): Should we do something special to make sure
 	// we don't print f.Log statements again with runFuzzing, since we already
 	// would have printed them when we ran runFuzzTargets (ie. seed corpus run)?
 	if len(fuzzTargets) == 0 || *matchFuzz == "" {
-		return false, 0, true
+		return true
 	}
 	m := newMatcher(deps.MatchString, *matchFuzz, "-test.fuzz")
 	tctx := newTestContext(1, m)
@@ -617,17 +617,23 @@ func runFuzzing(deps testDeps, fuzzTargets []InternalFuzzTarget) (ran bool, matc
 	}
 	var target *InternalFuzzTarget
 	var targetName string
+	var matched []string
 	for i := range fuzzTargets {
 		name, ok, _ := tctx.match.fullName(nil, fuzzTargets[i].Name)
 		if !ok {
 			continue
 		}
-		matched++
+		matched = append(matched, name)
 		target = &fuzzTargets[i]
 		targetName = name
 	}
-	if matched != 1 {
-		return false, matched, true
+	if len(matched) == 0 {
+		fmt.Fprintln(os.Stderr, "testing: warning: no targets to fuzz")
+		return true
+	}
+	if len(matched) > 1 {
+		fmt.Fprintf(os.Stderr, "testing: will not fuzz, -fuzz matches more than one target: %v\n", matched)
+		return false
 	}
 
 	f := &F{
@@ -649,7 +655,7 @@ func runFuzzing(deps testDeps, fuzzTargets []InternalFuzzTarget) (ran bool, matc
 	}
 	go fRunner(f, target.Fn)
 	<-f.signal
-	return f.ran, matched, !f.failed
+	return !f.failed
 }
 
 // fRunner wraps a call to a fuzz target and ensures that cleanup functions are
diff --git a/src/testing/testing.go b/src/testing/testing.go
index 5e66a0610b..f4d2b26650 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -1634,14 +1634,7 @@ func (m *M) Run() (code int) {
 		}
 	}
 
-	fuzzingRan, fuzzingMatched, fuzzingOk := runFuzzing(m.deps, m.fuzzTargets)
-	if *matchFuzz != "" && !fuzzingRan {
-		if fuzzingMatched == 0 {
-			fmt.Fprintln(os.Stderr, "testing: warning: no targets to fuzz")
-		} else {
-			fmt.Fprintln(os.Stderr, "testing: warning: will not fuzz, -fuzz matches more than one target")
-		}
-	}
+	fuzzingOk := runFuzzing(m.deps, m.fuzzTargets)
 	if !*isFuzzWorker && !fuzzingOk {
 		fmt.Println("FAIL")
 		if *isFuzzWorker {