diff --git a/tcp_mux_multi_test.go b/tcp_mux_multi_test.go
index a73252c..7fb0a09 100644
--- a/tcp_mux_multi_test.go
+++ b/tcp_mux_multi_test.go
@@ -7,6 +7,7 @@
 package ice
 
 import (
+	"errors"
 	"io"
 	"net"
 	"testing"
@@ -126,3 +127,142 @@ func TestMultiTCPMux_NoDeadlockWhenClosingUnusedPacketConn(t *testing.T) {
 	require.Nil(t, conn, "should receive nil because mux is closed")
 	require.Equal(t, io.ErrClosedPipe, err, "should receive error because mux is closed")
 }
+
+func TestMultiTCPMux_GetConnByUfrag_NoMuxes(t *testing.T) {
+	multi := NewMultiTCPMuxDefault() // no muxes
+
+	pc, err := multi.GetConnByUfrag("ufrag", false, net.IP{127, 0, 0, 1})
+	require.Nil(t, pc)
+	require.ErrorIs(t, err, errNoTCPMuxAvailable)
+}
+
+func TestMultiTCPMux_GetConnByUfrag_FromAnyMux(t *testing.T) {
+	logger := logging.NewDefaultLoggerFactory().NewLogger("ice")
+
+	l1, err := net.ListenTCP("tcp", &net.TCPAddr{IP: net.IP{127, 0, 0, 1}, Port: 0})
+	require.NoError(t, err)
+	defer func() {
+		_ = l1.Close()
+	}()
+
+	mux1 := NewTCPMuxDefault(TCPMuxParams{
+		Listener:       l1,
+		Logger:         logger,
+		ReadBufferSize: 8,
+	})
+
+	l2, err := net.ListenTCP("tcp", &net.TCPAddr{IP: net.IP{127, 0, 0, 1}, Port: 0})
+	require.NoError(t, err)
+	defer func() {
+		_ = l2.Close()
+	}()
+
+	mux2 := NewTCPMuxDefault(TCPMuxParams{
+		Listener:       l2,
+		Logger:         logger,
+		ReadBufferSize: 8,
+	})
+
+	multi := NewMultiTCPMuxDefault(mux1, mux2)
+	defer func() { _ = multi.Close() }()
+
+	pc, err := multi.GetConnByUfrag("myufrag", false, net.IP{127, 0, 0, 1})
+	require.NoError(t, err)
+	require.NotNil(t, pc)
+
+	pcAddr, ok := pc.LocalAddr().(*net.TCPAddr)
+	require.True(t, ok, "packet conn addr should be *net.TCPAddr")
+
+	m1Addr, ok := mux1.LocalAddr().(*net.TCPAddr)
+	require.True(t, ok, "mux1 local addr should be *net.TCPAddr")
+
+	m2Addr, ok := mux2.LocalAddr().(*net.TCPAddr)
+	require.True(t, ok, "mux2 local addr should be *net.TCPAddr")
+
+	isFromMux1 := pcAddr.Port == m1Addr.Port && pcAddr.IP.Equal(m1Addr.IP)
+	isFromMux2 := pcAddr.Port == m2Addr.Port && pcAddr.IP.Equal(m2Addr.IP)
+	require.True(t, isFromMux1 || isFromMux2, "conn must come from one of the underlying muxes")
+}
+
+func TestMultiTCPMux_GetAllConns_NoMuxes(t *testing.T) {
+	multi := NewMultiTCPMuxDefault() // no underlying TCPMux instances
+
+	conns, err := multi.GetAllConns("ufrag", false, net.IP{127, 0, 0, 1})
+
+	require.Nil(t, conns)
+	require.ErrorIs(t, err, errNoTCPMuxAvailable)
+}
+
+var (
+	errTCPMuxCloseBoom   = errors.New("tcp mux close boom")
+	errTCPMuxCloseFirst  = errors.New("first tcp mux close failed")
+	errTCPMuxCloseSecond = errors.New("second tcp mux close failed")
+)
+
+type closeErrTCPMux struct {
+	TCPMux
+	ret error
+}
+
+func (w *closeErrTCPMux) Close() error {
+	_ = w.TCPMux.Close()
+
+	return w.ret
+}
+
+func TestMultiTCPMux_Close_PropagatesError_FromWrappedMux(t *testing.T) {
+	logger := logging.NewDefaultLoggerFactory().NewLogger("ice")
+
+	// first mux: normal close (nil)
+	l1, err := net.ListenTCP("tcp", &net.TCPAddr{IP: net.IP{127, 0, 0, 1}, Port: 0})
+	require.NoError(t, err)
+	mux1 := NewTCPMuxDefault(TCPMuxParams{
+		Listener:       l1,
+		Logger:         logger,
+		ReadBufferSize: 8,
+	})
+
+	// second mux: Close() returns injected error
+	l2, err := net.ListenTCP("tcp", &net.TCPAddr{IP: net.IP{127, 0, 0, 1}, Port: 0})
+	require.NoError(t, err)
+	mux2Real := NewTCPMuxDefault(TCPMuxParams{
+		Listener:       l2,
+		Logger:         logger,
+		ReadBufferSize: 8,
+	})
+	mux2 := &closeErrTCPMux{TCPMux: mux2Real, ret: errTCPMuxCloseBoom}
+
+	multi := NewMultiTCPMuxDefault(mux1, mux2)
+
+	got := multi.Close()
+	require.ErrorIs(t, got, errTCPMuxCloseBoom)
+}
+
+func TestMultiTCPMux_Close_LastErrorWins_FromWrappedMuxes(t *testing.T) {
+	logger := logging.NewDefaultLoggerFactory().NewLogger("ice")
+
+	// first mux: error1
+	la, err := net.ListenTCP("tcp", &net.TCPAddr{IP: net.IP{127, 0, 0, 1}, Port: 0})
+	require.NoError(t, err)
+	mux1Real := NewTCPMuxDefault(TCPMuxParams{
+		Listener:       la,
+		Logger:         logger,
+		ReadBufferSize: 8,
+	})
+	mux1 := &closeErrTCPMux{TCPMux: mux1Real, ret: errTCPMuxCloseFirst}
+
+	// second mux: error2 (last error should be returned)
+	lb, err := net.ListenTCP("tcp", &net.TCPAddr{IP: net.IP{127, 0, 0, 1}, Port: 0})
+	require.NoError(t, err)
+	mux2Real := NewTCPMuxDefault(TCPMuxParams{
+		Listener:       lb,
+		Logger:         logger,
+		ReadBufferSize: 8,
+	})
+	mux2 := &closeErrTCPMux{TCPMux: mux2Real, ret: errTCPMuxCloseSecond}
+
+	multi := NewMultiTCPMuxDefault(mux1, mux2)
+
+	got := multi.Close()
+	require.ErrorIs(t, got, errTCPMuxCloseSecond)
+}