net: convert TestTCPServer to use subtests

My fix in CL 202618 inadvertently violated an invariant in the inner
loop of TestTCPServer (namely, that len(trchs) == i). That causes a
panic when one or more of the channels is omitted due to a flake.

Instead of trying to fix up the test, let's just factor out a subtest
and skip the whole thing if the transceiver's Dial flakes out.

Updates #32919

Change-Id: Ib6f274a44194311c8c5a2faf19f586cc9eccfd4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/202561
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/server_test.go

@@ -56,79 +56,79 @@ func TestTCPServer(t *testing.T) {
 	const N = 3
 
 	for i, tt := range tcpServerTests {
-		if !testableListenArgs(tt.snet, tt.saddr, tt.taddr) {
-			t.Logf("skipping %s test", tt.snet+" "+tt.saddr+"<-"+tt.taddr)
-			continue
-		}
-
-		ln, err := Listen(tt.snet, tt.saddr)
-		if err != nil {
-			if perr := parseDialError(err); perr != nil {
-				t.Error(perr)
+		t.Run(tt.snet+" "+tt.saddr+"<-"+tt.taddr, func(t *testing.T) {
+			if !testableListenArgs(tt.snet, tt.saddr, tt.taddr) {
+				t.Skip("not testable")
 			}
-			t.Fatal(err)
-		}
 
-		var lss []*localServer
-		var tpchs []chan error
-		defer func() {
-			for _, ls := range lss {
-				ls.teardown()
-			}
-		}()
-		for i := 0; i < N; i++ {
-			ls, err := (&streamListener{Listener: ln}).newLocalServer()
+			ln, err := Listen(tt.snet, tt.saddr)
 			if err != nil {
+				if perr := parseDialError(err); perr != nil {
+					t.Error(perr)
+				}
 				t.Fatal(err)
 			}
-			lss = append(lss, ls)
-			tpchs = append(tpchs, make(chan error, 1))
-		}
-		for i := 0; i < N; i++ {
-			ch := tpchs[i]
-			handler := func(ls *localServer, ln Listener) { transponder(ln, ch) }
-			if err := lss[i].buildup(handler); err != nil {
-				t.Fatal(err)
-			}
-		}
 
-		var trchs []chan error
-		for i := 0; i < N; i++ {
-			_, port, err := SplitHostPort(lss[i].Listener.Addr().String())
-			if err != nil {
-				t.Fatal(err)
+			var lss []*localServer
+			var tpchs []chan error
+			defer func() {
+				for _, ls := range lss {
+					ls.teardown()
+				}
+			}()
+			for i := 0; i < N; i++ {
+				ls, err := (&streamListener{Listener: ln}).newLocalServer()
+				if err != nil {
+					t.Fatal(err)
+				}
+				lss = append(lss, ls)
+				tpchs = append(tpchs, make(chan error, 1))
 			}
-			d := Dialer{Timeout: someTimeout}
-			c, err := d.Dial(tt.tnet, JoinHostPort(tt.taddr, port))
-			if err != nil {
-				if perr := parseDialError(err); perr != nil {
-					t.Error(perr)
+			for i := 0; i < N; i++ {
+				ch := tpchs[i]
+				handler := func(ls *localServer, ln Listener) { transponder(ln, ch) }
+				if err := lss[i].buildup(handler); err != nil {
+					t.Fatal(err)
 				}
-				if tt.taddr == "::1" && os.Getenv("GO_BUILDER_NAME") == "darwin-amd64-10_12" && os.IsTimeout(err) {
-					// A suspected kernel bug in macOS 10.12 occasionally results in
-					// "i/o timeout" errors when dialing address ::1. The errors have not
-					// been observed on newer versions of the OS, so we don't plan to work
-					// around them. See https://golang.org/issue/32919.
-					t.Logf("ignoring error on known-flaky macOS 10.12 builder: %v", err)
-					continue
+			}
+
+			var trchs []chan error
+			for i := 0; i < N; i++ {
+				_, port, err := SplitHostPort(lss[i].Listener.Addr().String())
+				if err != nil {
+					t.Fatal(err)
 				}
-				t.Fatal(err)
+				d := Dialer{Timeout: someTimeout}
+				c, err := d.Dial(tt.tnet, JoinHostPort(tt.taddr, port))
+				if err != nil {
+					if perr := parseDialError(err); perr != nil {
+						t.Error(perr)
+					}
+					if tt.taddr == "::1" && os.Getenv("GO_BUILDER_NAME") == "darwin-amd64-10_12" && os.IsTimeout(err) {
+						// A suspected kernel bug in macOS 10.12 occasionally results in
+						// "i/o timeout" errors when dialing address ::1. The errors have not
+						// been observed on newer versions of the OS, so we don't plan to work
+						// around them. See https://golang.org/issue/32919.
+						t.Skipf("skipping due to error on known-flaky macOS 10.12 builder: %v", err)
+					}
+					t.Fatal(err)
+				}
+				defer c.Close()
+				trchs = append(trchs, make(chan error, 1))
+				go transceiver(c, []byte("TCP SERVER TEST"), trchs[i])
 			}
-			defer c.Close()
-			trchs = append(trchs, make(chan error, 1))
-			go transceiver(c, []byte("TCP SERVER TEST"), trchs[i])
-		}
 
-		for _, ch := range trchs {
-			for err := range ch {
-				t.Errorf("#%d: %v", i, err)
+			for _, ch := range trchs {
+				for err := range ch {
+					t.Errorf("#%d: %v", i, err)
+				}
 			}
-		}
-		for _, ch := range tpchs {
-			for err := range ch {
-				t.Errorf("#%d: %v", i, err)
+			for _, ch := range tpchs {
+				for err := range ch {
+					t.Errorf("#%d: %v", i, err)
+				}
 			}
-		}
+		})
 	}
 }