all: fix "result not used" vet warnings

For tests, assign to _.
For benchmarks, assign to a sink.

Updates #11041

Change-Id: I87c5543245c7bc74dceb38902f4551768dd37948
Reviewed-on: https://go-review.googlesource.com/27116
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/math/big/decimal_test.go

@@ -105,12 +105,14 @@ func TestDecimalRounding(t *testing.T) {
 	}
 }
 
+var sink string
+
 func BenchmarkDecimalConversion(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		for shift := -100; shift <= +100; shift++ {
 			var d decimal
 			d.init(natOne, shift)
-			d.String()
+			sink = d.String()
 		}
 	}
 }

src/net/dnsmsg_test.go

@@ -117,7 +117,7 @@ func TestDNSParseSRVReply(t *testing.T) {
 	if !ok {
 		t.Fatal("unpacking packet failed")
 	}
-	msg.String() // exercise this code path
+	_ = msg.String() // exercise this code path
 	if g, e := len(msg.answer), 5; g != e {
 		t.Errorf("len(msg.answer) = %d; want %d", g, e)
 	}
@@ -165,7 +165,7 @@ func TestDNSParseCorruptSRVReply(t *testing.T) {
 	if !ok {
 		t.Fatal("unpacking packet failed")
 	}
-	msg.String() // exercise this code path
+	_ = msg.String() // exercise this code path
 	if g, e := len(msg.answer), 5; g != e {
 		t.Errorf("len(msg.answer) = %d; want %d", g, e)
 	}

src/net/ip_test.go

@@ -242,13 +242,15 @@ func TestIPString(t *testing.T) {
 	}
 }
 
+var sink string
+
 func BenchmarkIPString(b *testing.B) {
 	testHookUninstaller.Do(uninstallTestHooks)
 
 	for i := 0; i < b.N; i++ {
 		for _, tt := range ipStringTests {
 			if tt.in != nil {
-				tt.in.String()
+				sink = tt.in.String()
 			}
 		}
 	}
@@ -299,7 +301,7 @@ func BenchmarkIPMaskString(b *testing.B) {
 
 	for i := 0; i < b.N; i++ {
 		for _, tt := range ipMaskStringTests {
-			tt.in.String()
+			sink = tt.in.String()
 		}
 	}
 }

src/time/time_test.go

@@ -891,7 +891,7 @@ func TestLocationRace(t *testing.T) {
 	go func() {
 		c <- Now().String()
 	}()
-	Now().String()
+	_ = Now().String()
 	<-c
 	Sleep(100 * Millisecond)