net: don't run TestTCPBig unconditionally

The test requires tons of memory and results various failures, mainly
runtime errors and process termination by SIGKILL, caused by resource
exhaustion when the node under test doesn't have much resources.

This change makes use of -tcpbig flag to enable the test.

Change-Id: Id53fa5d88543e2e60ca9bb4f55a1914ccca844e1
Reviewed-on: https://go-review.googlesource.com/33254Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/main_test.go

@@ -24,6 +24,8 @@ var (
 )
 
 var (
+	testTCPBig = flag.Bool("tcpbig", false, "whether to test massive size of data per read or write call on TCP connection")
+
 	testDNSFlood = flag.Bool("dnsflood", false, "whether to test DNS query flooding")
 
 	// If external IPv4 connectivity exists, we can try dialing

src/net/tcpsock_test.go

@@ -670,8 +670,8 @@ func TestTCPSelfConnect(t *testing.T) {
 // Test that >32-bit reads work on 64-bit systems.
 // On 32-bit systems this tests that maxint reads work.
 func TestTCPBig(t *testing.T) {
-	if testing.Short() {
-		t.Skip("skipping test in short mode")
+	if !*testTCPBig {
+		t.Skip("test disabled; use -tcpbig to enable")
 	}
 
 	for _, writev := range []bool{false, true} {