runtime: rename TestPreemptM to TestSignalM

TestPreemptM doesn't test preemptM, it tests signalM. Rename it and
co-locate it with the other tests related to signals.

Change-Id: I7b95f2ba96530c49cfa8d5bf33282946b5f2d9af
Reviewed-on: https://go-review.googlesource.com/c/go/+/203891
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/crash_unix_test.go

@@ -16,6 +16,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
+	"sync"
 	"syscall"
 	"testing"
 	"unsafe"
@@ -309,3 +310,26 @@ func TestSignalDuringExec(t *testing.T) {
 		t.Fatalf("want %s, got %s\n", want, output)
 	}
 }
+
+func TestSignalM(t *testing.T) {
+	var want, got int64
+	var wg sync.WaitGroup
+	ready := make(chan *runtime.M)
+	wg.Add(1)
+	go func() {
+		runtime.LockOSThread()
+		want, got = runtime.WaitForSigusr1(func(mp *runtime.M) {
+			ready <- mp
+		}, 1e9)
+		runtime.UnlockOSThread()
+		wg.Done()
+	}()
+	waitingM := <-ready
+	runtime.SendSigusr1(waitingM)
+	wg.Wait()
+	if got == -1 {
+		t.Fatal("signalM signal not received")
+	} else if want != got {
+		t.Fatalf("signal sent to M %d, but received on M %d", want, got)
+	}
+}

src/runtime/preemptm_test.go

-// Copyright 2019 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
-
-package runtime_test
-
-import (
-	"runtime"
-	"sync"
-	"testing"
-)
-
-func TestPreemptM(t *testing.T) {
-	var want, got int64
-	var wg sync.WaitGroup
-	ready := make(chan *runtime.M)
-	wg.Add(1)
-	go func() {
-		runtime.LockOSThread()
-		want, got = runtime.WaitForSigusr1(func(mp *runtime.M) {
-			ready <- mp
-		}, 1e9)
-		runtime.UnlockOSThread()
-		wg.Done()
-	}()
-	runtime.SendSigusr1(<-ready)
-	wg.Wait()
-	if got == -1 {
-		t.Fatal("preemptM signal not received")
-	} else if want != got {
-		t.Fatalf("signal sent to M %d, but received on M %d", want, got)
-	}
-}