testing: clean up remaining TempDir issues from CL 231958

Updates #38850

Change-Id: I33f48762f5520eb0c0a841d8ca1ccdd65ecc20c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/234583
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/math/big/link_test.go

@@ -20,8 +20,9 @@ func TestLinkerGC(t *testing.T) {
 		t.Skip("skipping in short mode")
 	}
 	t.Parallel()
+	tmp := t.TempDir()
 	goBin := testenv.GoToolPath(t)
-	goFile := filepath.Join(t.TempDir(), "x.go")
+	goFile := filepath.Join(tmp, "x.go")
 	file := []byte(`package main
 import _ "math/big"
 func main() {}
@@ -30,13 +31,13 @@ func main() {}
 		t.Fatal(err)
 	}
 	cmd := exec.Command(goBin, "build", "-o", "x.exe", "x.go")
-	cmd.Dir = t.TempDir()
+	cmd.Dir = tmp
 	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Fatalf("compile: %v, %s", err, out)
 	}
 
 	cmd = exec.Command(goBin, "tool", "nm", "x.exe")
-	cmd.Dir = t.TempDir()
+	cmd.Dir = tmp
 	nm, err := cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("nm: %v, %s", err, nm)

src/os/readfrom_linux_test.go

@@ -249,14 +249,15 @@ func newCopyFileRangeTest(t *testing.T, size int64) (dst, src *File, data []byte
 	t.Helper()
 
 	hook = hookCopyFileRange(t)
+	tmp := t.TempDir()
 
-	src, err := Create(filepath.Join(t.TempDir(), "src"))
+	src, err := Create(filepath.Join(tmp, "src"))
 	if err != nil {
 		t.Fatal(err)
 	}
 	t.Cleanup(func() { src.Close() })
 
-	dst, err = Create(filepath.Join(t.TempDir(), "dst"))
+	dst, err = Create(filepath.Join(tmp, "dst"))
 	if err != nil {
 		t.Fatal(err)
 	}

src/testing/testing.go

@@ -822,11 +822,10 @@ var tempDirReplacer struct {
 }
 
 // TempDir returns a temporary directory for the test to use.
-// It is lazily created on first access, and calls t.Fatal if the directory
-// creation fails.
-// Subsequent calls to t.TempDir return the same directory.
 // The directory is automatically removed by Cleanup when the test and
 // all its subtests complete.
+// Each subsequent call to t.TempDir returns a unique directory;
+// if the directory creation fails, TempDir terminates the test by calling Fatal.
 func (c *common) TempDir() string {
 	// Use a single parent directory for all the temporary directories
 	// created by a test, each numbered sequentially.