diff --git a/internal/multiplex/mux_test.go b/internal/multiplex/mux_test.go
new file mode 100644
index 0000000..9f6b2fb
--- /dev/null
+++ b/internal/multiplex/mux_test.go
@@ -0,0 +1,158 @@
+package multiplex
+
+import (
+	"bytes"
+	"github.com/cbeuw/Cloak/internal/util"
+	"github.com/cbeuw/connutil"
+	"io"
+	"math/rand"
+	"net"
+	"sync"
+	"testing"
+	"time"
+)
+
+func serveEcho(l net.Listener) {
+	for {
+		conn, err := l.Accept()
+		if err != nil {
+			// TODO: pass the error back
+			return
+		}
+		go func() {
+			_, err := io.Copy(conn, conn)
+			if err != nil {
+				// TODO: pass the error back
+				return
+			}
+		}()
+	}
+}
+
+type connPair struct {
+	clientConn net.Conn
+	serverConn net.Conn
+}
+
+func makeSessionPair(numConn int) (*Session, *Session, []*connPair) {
+	sessionKey := [32]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31}
+	sessionId := 1
+	obfuscator, _ := MakeObfuscator(E_METHOD_CHACHA20_POLY1305, sessionKey, true)
+	clientConfig := SessionConfig{
+		Obfuscator: obfuscator,
+		Valve:      nil,
+		UnitRead:   util.ReadTLS,
+		Unordered:  false,
+	}
+	serverConfig := clientConfig
+
+	clientSession := MakeSession(uint32(sessionId), clientConfig)
+	serverSession := MakeSession(uint32(sessionId), serverConfig)
+
+	paris := make([]*connPair, numConn)
+	for i := 0; i < numConn; i++ {
+		clientConn, serverConn := connutil.AsyncPipe()
+		paris[i] = &connPair{
+			clientConn: clientConn,
+			serverConn: serverConn,
+		}
+		clientSession.AddConnection(clientConn)
+		serverSession.AddConnection(serverConn)
+	}
+	return clientSession, serverSession, paris
+}
+
+func runEchoTest(t *testing.T, streams []*Stream) {
+	const testDataLen = 16384
+	var wg sync.WaitGroup
+	for _, stream := range streams {
+		wg.Add(1)
+		go func(stream *Stream) {
+			testData := make([]byte, testDataLen)
+			rand.Read(testData)
+
+			n, err := stream.Write(testData)
+			if n != testDataLen {
+				t.Fatalf("written only %v, err %v", n, err)
+			}
+
+			recvBuf := make([]byte, testDataLen)
+			_, err = io.ReadFull(stream, recvBuf)
+			if err != nil {
+				t.Fatalf("failed to read back: %v", err)
+			}
+
+			if !bytes.Equal(testData, recvBuf) {
+				t.Fatalf("echoed data not correct")
+			}
+			wg.Done()
+		}(stream)
+	}
+	wg.Wait()
+}
+
+func TestMultiplex(t *testing.T) {
+	const numStreams = 2000 // -race option limits the number of goroutines to 8192
+	const numConns = 4
+
+	clientSession, serverSession, _ := makeSessionPair(numConns)
+	go serveEcho(serverSession)
+
+	streams := make([]*Stream, numStreams)
+	for i := 0; i < numStreams; i++ {
+		stream, err := clientSession.OpenStream()
+		if err != nil {
+			t.Fatalf("failed to open stream: %v", err)
+		}
+		streams[i] = stream
+	}
+
+	//test echo
+	runEchoTest(t, streams)
+	if clientSession.streamCount() != numStreams {
+		t.Errorf("client stream count is wrong: %v", clientSession.streamCount())
+	}
+	if serverSession.streamCount() != numStreams {
+		t.Errorf("server stream count is wrong: %v", serverSession.streamCount())
+	}
+
+	// close one stream
+	closing, streams := streams[0], streams[1:]
+	err := closing.Close()
+	if err != nil {
+		t.Errorf("couldn't close a stream")
+	}
+	_, err = closing.Write([]byte{0})
+	if err != ErrBrokenStream {
+		t.Errorf("expecting error %v, got %v", ErrBrokenStream, err)
+	}
+	_, err = closing.Read(make([]byte, 1))
+	if err != ErrBrokenStream {
+		t.Errorf("expecting error %v, got %v", ErrBrokenStream, err)
+	}
+
+}
+
+func TestMux_StreamClosing(t *testing.T) {
+	clientSession, serverSession, _ := makeSessionPair(1)
+	go serveEcho(serverSession)
+
+	// read after closing stream
+	testData := make([]byte, 128)
+	recvBuf := make([]byte, 128)
+	toBeClosed, _ := clientSession.OpenStream()
+	_, err := toBeClosed.Write(testData) // should be echoed back
+	if err != nil {
+		t.Errorf("can't write to stream: %v", err)
+	}
+
+	time.Sleep(500 * time.Millisecond)
+	_ = toBeClosed.Close()
+	_, err = io.ReadFull(toBeClosed, recvBuf)
+	if err != nil {
+		t.Errorf("can't read residual data on stream: %v", err)
+	}
+	if !bytes.Equal(testData, recvBuf) {
+		t.Errorf("incorrect data read back")
+	}
+}