tests: add missing calls to t.Helper()

In a few places, we added calls t.Helper()
properly in test only funcs.

In the test safeBuf struct, we added support
for t.Helper() in all the receiver funcs

mux_test.go

@@ -51,10 +51,7 @@ func TestMux_serve(t *testing.T) {
 	})
 	t.Run("default-route", func(t *testing.T) {
 		assert, require := assert.New(t), require.New(t)
-		buf := &safeBuf{
-			mu:  &sync.Mutex{},
-			buf: &strings.Builder{},
-		}
+		buf := testSafeBuf(t)
 		testLogger := hclog.New(&hclog.LoggerOptions{
 			Name:   "TestServer_Run-logger",
 			Level:  hclog.Debug,

testing.go

@@ -184,6 +184,7 @@ func testAddRequestPacket(t *testing.T, m AddMessage) *packet {
 }
 
 func testRequestEnvelope(t *testing.T, messageID int) *ber.Packet {
+	t.Helper()
 	p := ber.Encode(ber.ClassUniversal, ber.TypeConstructed, ber.TagSequence, nil, "LDAP Request")
 	p.AppendChild(ber.NewInteger(ber.ClassUniversal, ber.TypePrimitive, ber.TagInteger, int64(messageID), "MessageID"))
 	return p
@@ -253,26 +254,30 @@ func TestEncodeString(t *testing.T, tag ber.Tag, s string, opt ...Option) string
 }
 
 type safeBuf struct {
+	t   *testing.T
 	buf *strings.Builder
-	mu  *sync.Mutex
+	mu  *sync.RWMutex
 }
 
 func testSafeBuf(t *testing.T) *safeBuf {
 	t.Helper()
 	return &safeBuf{
-		mu:  &sync.Mutex{},
+		t:   t,
+		mu:  &sync.RWMutex{},
 		buf: &strings.Builder{},
 	}
 }
 
 func (w *safeBuf) Write(p []byte) (n int, err error) {
+	w.t.Helper()
 	w.mu.Lock()
 	defer w.mu.Unlock()
 	return w.buf.Write(p)
 }
 
 func (w *safeBuf) String() string {
-	w.mu.Lock()
-	defer w.mu.Unlock()
+	w.t.Helper()
+	w.mu.RLock()
+	defer w.mu.RUnlock()
 	return w.buf.String()
 }