internal/zstd: abstract zstd binary path lookup in tests

This commit introduces a function findZstd which is responsible for locating the
zstd executable used by fuzz and unit tests. Previously, the explicit path
"/usr/bin/zstd" was hard-coded into test cases, which could lead to skipped tests
on systems where zstd is located elsewhere or not present at that specific path.

Fixes #64000

src/internal/zstd/fuzz_test.go

@@ -43,9 +43,7 @@ func FuzzReader(f *testing.F) {
 // explore the space of decompressor behavior, since it can't see
 // what the compressor is doing. But it's better than nothing.
 func FuzzDecompressor(f *testing.F) {
-	if _, err := os.Stat("/usr/bin/zstd"); err != nil {
-		f.Skip("skipping because /usr/bin/zstd does not exist")
-	}
+	zstd := findZstd(f)
 
 	for _, test := range tests {
 		f.Add([]byte(test.uncompressed))
@@ -61,7 +59,7 @@ func FuzzDecompressor(f *testing.F) {
 	f.Add(bigData(f))
 
 	f.Fuzz(func(t *testing.T, b []byte) {
-		cmd := exec.Command("/usr/bin/zstd", "-z")
+		cmd := exec.Command(zstd, "-z")
 		cmd.Stdin = bytes.NewReader(b)
 		var compressed bytes.Buffer
 		cmd.Stdout = &compressed
@@ -84,9 +82,7 @@ func FuzzDecompressor(f *testing.F) {
 // Fuzz test to check that if we can decompress some data,
 // so can zstd, and that we get the same result.
 func FuzzReverse(f *testing.F) {
-	if _, err := os.Stat("/usr/bin/zstd"); err != nil {
-		f.Skip("skipping because /usr/bin/zstd does not exist")
-	}
+	zstd := findZstd(f)
 
 	for _, test := range tests {
 		f.Add([]byte(test.compressed))
@@ -100,7 +96,7 @@ func FuzzReverse(f *testing.F) {
 		r := NewReader(bytes.NewReader(b))
 		goExp, goErr := io.ReadAll(r)
 
-		cmd := exec.Command("/usr/bin/zstd", "-d")
+		cmd := exec.Command(zstd, "-d")
 		cmd.Stdin = bytes.NewReader(b)
 		var uncompressed bytes.Buffer
 		cmd.Stdout = &uncompressed

src/internal/zstd/zstd_test.go

@@ -167,10 +167,17 @@ func bigData(t testing.TB) []byte {
 	return bigDataBytes
 }
 
+func findZstd(t testing.TB) string {
+	zstd, err := exec.LookPath("zstd")
+	if err != nil {
+		t.Skip("skipping because zstd not found")
+	}
+	return zstd
+}
+
 var (
 	zstdBigOnce  sync.Once
 	zstdBigBytes []byte
-	zstdBigSkip  bool
 	zstdBigErr   error
 )
 
@@ -180,13 +187,10 @@ var (
 func zstdBigData(t testing.TB) []byte {
 	input := bigData(t)
 
-	zstdBigOnce.Do(func() {
-		if _, err := os.Stat("/usr/bin/zstd"); err != nil {
-			zstdBigSkip = true
-			return
-		}
+	zstd := findZstd(t)
 
-		cmd := exec.Command("/usr/bin/zstd", "-z")
+	zstdBigOnce.Do(func() {
+		cmd := exec.Command(zstd, "-z")
 		cmd.Stdin = bytes.NewReader(input)
 		var compressed bytes.Buffer
 		cmd.Stdout = &compressed
@@ -198,9 +202,6 @@ func zstdBigData(t testing.TB) []byte {
 
 		zstdBigBytes = compressed.Bytes()
 	})
-	if zstdBigSkip {
-		t.Skip("skipping because /usr/bin/zstd does not exist")
-	}
 	if zstdBigErr != nil {
 		t.Fatal(zstdBigErr)
 	}
@@ -217,7 +218,7 @@ func TestLarge(t *testing.T) {
 	data := bigData(t)
 	compressed := zstdBigData(t)
 
-	t.Logf("/usr/bin/zstd compressed %d bytes to %d", len(data), len(compressed))
+	t.Logf("zstd compressed %d bytes to %d", len(data), len(compressed))
 
 	r := NewReader(bytes.NewReader(compressed))
 	got, err := io.ReadAll(r)