os/signal: skip the nohup test on darwin when running in tmux.

The nohup command doesn't work in tmux on darwin.

Fixes #5135.

Change-Id: I1c21073d8bd54b49dd6b0bad86ef088d6d8e7a5f
Reviewed-on: https://go-review.googlesource.com/13883Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/os/signal/signal_test.go

@@ -255,6 +255,12 @@ func TestNohup(t *testing.T) {
 
 	Stop(c)
 
+	// Skip the nohup test below when running in tmux on darwin, since nohup
+	// doesn't work correctly there. See issue #5135.
+	if runtime.GOOS == "darwin" && os.Getenv("TMUX") != "" {
+		t.Skip("Skipping nohup test due to running in tmux on darwin")
+	}
+
 	// Again, this time with nohup, assuming we can find it.
 	_, err := os.Stat("/usr/bin/nohup")
 	if err != nil {