tstest/integration: shorten test names

The maximum unix domain socket path length on darwin is 104 bytes,
including the trailing NUL.

On my machine, the path created by some newly added tests (6eecf3c9)
was too long, resulting in cryptic test failures.

Shorten the names of the tests, and add a check to make
the diagnosis easier next time.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

tstest/integration/integration_test.go

@@ -314,7 +314,7 @@ func TestAddPingRequest(t *testing.T) {
 
 // Issue 2434: when "down" (WantRunning false), tailscaled shouldn't
 // be connected to control.
-func TestNoControlConnectionWhenDown(t *testing.T) {
+func TestNoControlConnWhenDown(t *testing.T) {
 	t.Parallel()
 	bins := BuildTestBinaries(t)
 
@@ -361,7 +361,7 @@ func TestNoControlConnectionWhenDown(t *testing.T) {
 
 // Issue 2137: make sure Windows tailscaled works with the CLI alone,
 // without the GUI to kick off a Start.
-func TestOneNodeUp_WindowsStyle(t *testing.T) {
+func TestOneNodeUpWindowsStyle(t *testing.T) {
 	t.Parallel()
 	bins := BuildTestBinaries(t)
 
@@ -471,10 +471,14 @@ type testNode struct {
 // The node is not started automatically.
 func newTestNode(t *testing.T, env *testEnv) *testNode {
 	dir := t.TempDir()
+	sockFile := filepath.Join(dir, "tailscale.sock")
+	if len(sockFile) >= 104 {
+		t.Fatalf("sockFile path %q (len %v) is too long, must be < 104", sockFile, len(sockFile))
+	}
 	return &testNode{
 		env:       env,
 		dir:       dir,
-		sockFile:  filepath.Join(dir, "tailscale.sock"),
+		sockFile:  sockFile,
 		stateFile: filepath.Join(dir, "tailscale.state"),
 	}
 }