net: remove redundant test case for lookupIP with threadLimit

There is no reason to have the redundant test case TestDNSThreadLimt
because TestLookupIPDeadline does cover what we need to test with
-dnsflood flag and more.

Also this CL moves TestLookupIPDeadline into lookup_test.go to avoid
abusing to control the order of test case execution by using file name.

Change-Id: Ib417d7d3411c59d9352c03c996704d584368dc62
Reviewed-on: https://go-review.googlesource.com/2204
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: cixtor

src/net/lookup_test.go

@@ -9,8 +9,10 @@ package net
 
 import (
 	"flag"
+	"fmt"
 	"strings"
 	"testing"
+	"time"
 )
 
 var testExternal = flag.Bool("external", true, "allow use of external networks during long test")
@@ -229,3 +231,66 @@ func TestReverseAddress(t *testing.T) {
 		}
 	}
 }
+
+var testDNSFlood = flag.Bool("dnsflood", false, "whether to test dns query flooding")
+
+func TestLookupIPDeadline(t *testing.T) {
+	if !*testDNSFlood {
+		t.Skip("test disabled; use -dnsflood to enable")
+	}
+
+	const N = 5000
+	const timeout = 3 * time.Second
+	c := make(chan error, 2*N)
+	for i := 0; i < N; i++ {
+		name := fmt.Sprintf("%d.net-test.golang.org", i)
+		go func() {
+			_, err := lookupIPDeadline(name, time.Now().Add(timeout/2))
+			c <- err
+		}()
+		go func() {
+			_, err := lookupIPDeadline(name, time.Now().Add(timeout))
+			c <- err
+		}()
+	}
+	qstats := struct {
+		succeeded, failed         int
+		timeout, temporary, other int
+		unknown                   int
+	}{}
+	deadline := time.After(timeout + time.Second)
+	for i := 0; i < 2*N; i++ {
+		select {
+		case <-deadline:
+			t.Fatal("deadline exceeded")
+		case err := <-c:
+			switch err := err.(type) {
+			case nil:
+				qstats.succeeded++
+			case Error:
+				qstats.failed++
+				if err.Timeout() {
+					qstats.timeout++
+				}
+				if err.Temporary() {
+					qstats.temporary++
+				}
+				if !err.Timeout() && !err.Temporary() {
+					qstats.other++
+				}
+			default:
+				qstats.failed++
+				qstats.unknown++
+			}
+		}
+	}
+
+	// A high volume of DNS queries for sub-domain of golang.org
+	// would be coordinated by authoritative or recursive server,
+	// or stub resolver which implements query-response rate
+	// limitation, so we can expect some query successes and more
+	// failures including timeout, temporary and other here.
+	// As a rule, unknown must not be shown but it might possibly
+	// happen due to issue 4856 for now.
+	t.Logf("%v succeeded, %v failed (%v timeout, %v temporary, %v other, %v unknown)", qstats.succeeded, qstats.failed, qstats.timeout, qstats.temporary, qstats.other, qstats.unknown)
+}