net: add test for CL 17458

I thought that we avoided creating on-disk Unix sockets,
but I was mistaken. Use one to test CL 17458.

Fixes #11826.

Change-Id: Iaa1fb007b95fa6be48200586522a6d4789ecd346
Reviewed-on: https://go-review.googlesource.com/17725
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/unix_test.go

@@ -405,6 +405,42 @@ func TestUnixgramConnLocalAndRemoteNames(t *testing.T) {
 	}
 }
 
+func TestUnixUnlink(t *testing.T) {
+	if !testableNetwork("unix") {
+		t.Skip("unix test")
+	}
+	name := testUnixAddr()
+	l, err := Listen("unix", name)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(name); err != nil {
+		t.Fatalf("cannot stat unix socket after ListenUnix: %v", err)
+	}
+	f, _ := l.(*UnixListener).File()
+	l1, err := FileListener(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(name); err != nil {
+		t.Fatalf("cannot stat unix socket after FileListener: %v", err)
+	}
+	if err := l1.Close(); err != nil {
+		t.Fatalf("closing file listener: %v", err)
+	}
+	if _, err := os.Stat(name); err != nil {
+		t.Fatalf("cannot stat unix socket after closing FileListener: %v", err)
+	}
+	f.Close()
+	if _, err := os.Stat(name); err != nil {
+		t.Fatalf("cannot stat unix socket after closing FileListener and fd: %v", err)
+	}
+	l.Close()
+	if _, err := os.Stat(name); err == nil {
+		t.Fatal("closing unix listener did not remove unix socket")
+	}
+}
+
 // forceGoDNS forces the resolver configuration to use the pure Go resolver
 // and returns a fixup function to restore the old settings.
 func forceGoDNS() func() {