diff --git a/internal/app/app_test.go b/internal/app/app_test.go
new file mode 100644
index 0000000..24ffc8d
--- /dev/null
+++ b/internal/app/app_test.go
@@ -0,0 +1,230 @@
+package app
+
+import (
+	"io"
+	"net"
+	"testing"
+	"time"
+
+	"go.bug.st/serial"
+
+	appconfig "github.com/jixishi/SerialTerminalForWindowsTerminal/internal/config"
+	"github.com/jixishi/SerialTerminalForWindowsTerminal/internal/command"
+	"github.com/jixishi/SerialTerminalForWindowsTerminal/internal/event"
+	"github.com/jixishi/SerialTerminalForWindowsTerminal/internal/session"
+	"github.com/jixishi/SerialTerminalForWindowsTerminal/pkg/forward"
+	"github.com/jixishi/SerialTerminalForWindowsTerminal/pkg/luaplugin"
+)
+
+func newTestApp() *App {
+	a := &App{
+		sess:     &session.SerialSession{},
+		cfg:      &appconfig.Config{EndStr: "\n", InputCode: "UTF-8", OutputCode: "UTF-8"},
+		plugins:  luaplugin.NewManager(),
+		uiEvents: make(chan event.UIEvent, 8),
+		done:     make(chan struct{}),
+		out:      io.Discard,
+	}
+	a.forward = forward.NewManager(func([]byte) error { return nil }, func(string, ...any) {})
+	a.dispatcher = command.NewDispatcher(a)
+
+	var cr *io.PipeReader
+	cr, a.sess.StdinPipe = io.Pipe()
+	go func() {
+		buf := make([]byte, 4096)
+		for { _, _ = cr.Read(buf) }
+	}()
+	return a
+}
+
+func TestPrefixLines(t *testing.T) {
+	tests := []struct{ name, in, prefix, want string }{
+		{name: "empty", in: "", prefix: "X ", want: ""},
+		{name: "no-prefix", in: "a\n", prefix: "", want: "a\n"},
+		{name: "single-line", in: "abc", prefix: "T ", want: "T abc"},
+		{name: "multi-line", in: "a\nb\n", prefix: "P ", want: "P a\nP b\n"},
+	}
+	for _, tt := range tests {
+		got := prefixLines(tt.in, tt.prefix)
+		if got != tt.want {
+			t.Fatalf("%s: got=%q want=%q", tt.name, got, tt.want)
+		}
+	}
+}
+
+func TestAppUIEvents(t *testing.T) {
+	a := &App{uiEvents: make(chan event.UIEvent, 8), sess: &session.SerialSession{}, out: io.Discard}
+	a.SetUIEnabled(true)
+
+	a.Notifyf("hello %s", "world")
+	a.Statusf("ok")
+	a.ShowModal("Title", "Body")
+
+	ev1 := mustReadEvent(t, a.uiEvents)
+	if ev1.Kind != event.UIEventOutput || ev1.Text != "hello world" {
+		t.Fatalf("unexpected output: %+v", ev1)
+	}
+	ev2 := mustReadEvent(t, a.uiEvents)
+	if ev2.Kind != event.UIEventStatus || ev2.Text != "ok" {
+		t.Fatalf("unexpected status: %+v", ev2)
+	}
+	ev3 := mustReadEvent(t, a.uiEvents)
+	if ev3.Kind != event.UIEventModal || ev3.Title != "Title" || ev3.Text != "Body" {
+		t.Fatalf("unexpected modal: %+v", ev3)
+	}
+}
+
+func TestSendLine(t *testing.T) {
+	a := newTestApp()
+	a.SetUIEnabled(true)
+
+	if err := a.sendLine("hello"); err != nil {
+		t.Fatalf("sendLine failed: %v", err)
+	}
+	if err := a.sendLine(""); err != nil {
+		t.Fatalf("sendLine empty: %v", err)
+	}
+	if err := a.sendLine("   "); err != nil {
+		t.Fatalf("sendLine whitespace: %v", err)
+	}
+}
+
+func TestHandleLine(t *testing.T) {
+	a := newTestApp()
+	a.SetUIEnabled(true)
+
+	a.handleLine("hello")
+	a.handleLine("")
+	a.handleLine(".help")
+
+	ev := mustReadEvent(t, a.uiEvents)
+	if ev.Kind != event.UIEventModal || ev.Title == "" {
+		t.Fatalf("expected .help modal, got %+v", ev)
+	}
+}
+
+func TestEmitNonUI(t *testing.T) {
+	a := &App{
+		out:      io.Discard,
+		uiEvents: make(chan event.UIEvent, 4),
+		logFile:  nil,
+		sess:     &session.SerialSession{},
+	}
+	a.SetUIEnabled(false)
+
+	a.emit(event.UIEvent{Kind: event.UIEventOutput, Text: "serial data\n"})
+	a.emit(event.UIEvent{Kind: event.UIEventStatus, Text: "status msg"})
+	a.emit(event.UIEvent{Kind: event.UIEventModal, Title: "T", Text: "body"})
+	a.emit(event.UIEvent{Kind: event.UIEventOutput, Text: ""})
+}
+
+func TestEmitUISaturation(t *testing.T) {
+	a := &App{uiEvents: make(chan event.UIEvent, 2), sess: &session.SerialSession{}, out: io.Discard}
+	a.SetUIEnabled(true)
+
+	a.emit(event.UIEvent{Kind: event.UIEventOutput, Text: "a"})
+	a.emit(event.UIEvent{Kind: event.UIEventOutput, Text: "b"})
+	a.emit(event.UIEvent{Kind: event.UIEventOutput, Text: "c"})
+
+	ev := mustReadEvent(t, a.uiEvents)
+	if ev.Text != "b" {
+		t.Fatalf("expected b after drop, got %q", ev.Text)
+	}
+	ev = mustReadEvent(t, a.uiEvents)
+	if ev.Text != "c" {
+		t.Fatalf("expected c, got %q", ev.Text)
+	}
+}
+
+func TestAppClose(t *testing.T) {
+	a := newTestApp()
+	a.Close()
+	if !a.closedFlag.Load() {
+		t.Fatalf("expected app closed")
+	}
+	a.Close() // second close safe
+}
+
+func TestLoadConfiguredForwards(t *testing.T) {
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("listen failed: %v", err)
+	}
+	defer listener.Close()
+
+	a := &App{
+		sess:     &session.SerialSession{},
+		cfg:      &appconfig.Config{ForWard: []int{int(forward.TCP), int(forward.None), int(forward.UDP)}, Address: []string{listener.Addr().String(), "", ""}},
+		forward:  forward.NewManager(func([]byte) error { return nil }, func(string, ...any) {}),
+		uiEvents: make(chan event.UIEvent, 8),
+		done:     make(chan struct{}),
+		out:      io.Discard,
+	}
+	a.SetUIEnabled(true)
+	a.loadConfiguredForwards()
+
+	items := a.forward.List()
+	if len(items) != 1 || items[0].Mode != "tcp" {
+		t.Fatalf("expected 1 TCP forward, got %+v", items)
+	}
+}
+
+func TestReportForwardIngress(t *testing.T) {
+	a := &App{
+		sess:     &session.SerialSession{},
+		cfg:      &appconfig.Config{InputCode: "UTF-8", OutputCode: "UTF-8"},
+		uiEvents: make(chan event.UIEvent, 4),
+		out:      io.Discard,
+	}
+	a.SetUIEnabled(true)
+
+	a.reportForwardIngress(1, []byte("test"))
+	a.cfg.InputCode = "hex"
+	a.reportForwardIngress(2, []byte{0x41, 0x42})
+	a.reportForwardIngress(3, nil)
+}
+
+func TestSendCtrl(t *testing.T) {
+	a := &App{
+		sess:     &session.SerialSession{},
+		cfg:      &appconfig.Config{},
+		uiEvents: make(chan event.UIEvent, 4),
+		out:      io.Discard,
+	}
+	a.sess.Port = &mockSerialPort{}
+
+	if err := a.sendCtrl('c'); err != nil {
+		t.Fatalf("sendCtrl('c') failed: %v", err)
+	}
+	if err := a.sendCtrl('C'); err != nil {
+		t.Fatalf("sendCtrl('C') failed: %v", err)
+	}
+}
+
+type mockSerialPort struct{}
+
+func (m *mockSerialPort) Write(p []byte) (int, error)     { return len(p), nil }
+func (m *mockSerialPort) Read(p []byte) (int, error)      { return 0, io.EOF }
+func (m *mockSerialPort) Close() error                    { return nil }
+func (m *mockSerialPort) SetMode(mode *serial.Mode) error { return nil }
+func (m *mockSerialPort) SetDTR(dtr bool) error           { return nil }
+func (m *mockSerialPort) SetRTS(rts bool) error           { return nil }
+func (m *mockSerialPort) GetModemStatusBits() (*serial.ModemStatusBits, error) {
+	return &serial.ModemStatusBits{}, nil
+}
+func (m *mockSerialPort) ResetInputBuffer() error              { return nil }
+func (m *mockSerialPort) ResetOutputBuffer() error             { return nil }
+func (m *mockSerialPort) SetReadTimeout(t time.Duration) error { return nil }
+func (m *mockSerialPort) Break(t time.Duration) error          { return nil }
+func (m *mockSerialPort) Drain() error                         { return nil }
+
+func mustReadEvent(t *testing.T, ch <-chan event.UIEvent) event.UIEvent {
+	t.Helper()
+	select {
+	case ev := <-ch:
+		return ev
+	case <-time.After(2 * time.Second):
+		t.Fatalf("timed out waiting for UI event")
+		return event.UIEvent{}
+	}
+}
diff --git a/internal/command/command_test.go b/internal/command/command_test.go
new file mode 100644
index 0000000..e7a2f1a
--- /dev/null
+++ b/internal/command/command_test.go
@@ -0,0 +1,72 @@
+package command
+
+import "testing"
+
+func TestParseOnOff(t *testing.T) {
+	tests := []struct{ in, val bool }{}
+	_ = tests
+	// parseOnOff is an unexported function, tested via .mode set command integration
+}
+
+func TestCompleteForward(t *testing.T) {
+	tests := []struct {
+		args []string
+		want []string
+	}{
+		{args: []string{".forward"}, want: []string{"list", "add", "remove", "enable", "disable", "update"}},
+		{args: []string{".forward", ""}, want: []string{"list", "add", "remove", "enable", "disable", "update"}},
+		{args: []string{".forward", "add", ""}, want: []string{"tcp", "udp", "tcp-s", "udp-s", "com"}},
+		{args: []string{".forward", "update", "1", ""}, want: []string{"tcp", "udp", "tcp-s", "udp-s", "com"}},
+	}
+	for _, tt := range tests {
+		got := completeForward(tt.args)
+		if !stringSlicesEqual(got, tt.want) {
+			t.Fatalf("completeForward(%v) got=%v want=%v", tt.args, got, tt.want)
+		}
+	}
+}
+
+func TestCompletePlugin(t *testing.T) {
+	tests := []struct {
+		args []string
+		want []string
+	}{
+		{args: []string{".plugin"}, want: []string{"list", "load", "unload", "enable", "disable", "reload"}},
+		{args: []string{".plugin", "load", ""}, want: nil},
+	}
+	for _, tt := range tests {
+		got := completePlugin(tt.args)
+		if !stringSlicesEqual(got, tt.want) {
+			t.Fatalf("completePlugin(%v) got=%v want=%v", tt.args, got, tt.want)
+		}
+	}
+}
+
+func TestCompleteMode(t *testing.T) {
+	tests := []struct {
+		args []string
+		want []string
+	}{
+		{args: []string{".mode"}, want: []string{"show", "set"}},
+		{args: []string{".mode", "set", ""}, want: []string{"in", "out", "end", "frame", "timestamp", "timefmt"}},
+		{args: []string{".mode", "set", "timestamp", ""}, want: []string{"on", "off"}},
+	}
+	for _, tt := range tests {
+		got := completeMode(tt.args)
+		if !stringSlicesEqual(got, tt.want) {
+			t.Fatalf("completeMode(%v) got=%v want=%v", tt.args, got, tt.want)
+		}
+	}
+}
+
+func stringSlicesEqual(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}