diff --git a/internal/printer/driver_test.go b/internal/printer/driver_test.go
new file mode 100644
index 0000000..14d3c8e
--- /dev/null
+++ b/internal/printer/driver_test.go
@@ -0,0 +1,121 @@
+package printer
+
+import (
+	"image"
+	"image/color"
+	"math"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// Test 1: MockDriver.Print(validBitmap) saves a PNG to SaveDir and returns nil.
+func TestMockDriverPrintSavesPNG(t *testing.T) {
+	dir := t.TempDir()
+	m := NewMockDriver()
+	m.SaveDir = dir
+
+	// Create a small 8x4 1-bit bitmap (all black).
+	rowBytes := int(math.Ceil(8.0 / 8.0))
+	bitmap := make([]byte, rowBytes*4)
+	for i := range bitmap {
+		bitmap[i] = 0xFF // all black
+	}
+
+	if err := m.Print(bitmap, 8, 4); err != nil {
+		t.Fatalf("Print returned unexpected error: %v", err)
+	}
+
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatalf("ReadDir: %v", err)
+	}
+	found := false
+	for _, e := range entries {
+		if strings.HasPrefix(e.Name(), "hwlab-label-") && strings.HasSuffix(e.Name(), ".png") {
+			found = true
+			break
+		}
+	}
+	if !found {
+		t.Fatal("expected hwlab-label-*.png to be created in temp dir")
+	}
+}
+
+// Test 2: MockDriver.Print(nil) returns ErrEmptyBitmap without panicking.
+func TestMockDriverPrintNilBitmap(t *testing.T) {
+	m := NewMockDriver()
+	err := m.Print(nil, 0, 0)
+	if err != ErrEmptyBitmap {
+		t.Fatalf("expected ErrEmptyBitmap, got %v", err)
+	}
+}
+
+// Test 3: MockDriver.Connect() returns nil; Disconnect() returns nil.
+func TestMockDriverConnectDisconnect(t *testing.T) {
+	m := NewMockDriver()
+	if err := m.Connect(); err != nil {
+		t.Fatalf("Connect: %v", err)
+	}
+	if err := m.Disconnect(); err != nil {
+		t.Fatalf("Disconnect: %v", err)
+	}
+}
+
+// Test 4: ImageToRawBitmap returns byte slice of length ceil(width*height/8).
+func TestImageToRawBitmapLength(t *testing.T) {
+	cases := []struct {
+		w, h int
+	}{
+		{8, 4},
+		{7, 3},
+		{16, 1},
+		{384, 120},
+	}
+	for _, c := range cases {
+		img := image.NewGray(image.Rect(0, 0, c.w, c.h))
+		// Fill with a pattern: top half black, bottom half white.
+		for y := 0; y < c.h/2; y++ {
+			for x := 0; x < c.w; x++ {
+				img.SetGray(x, y, color.Gray{Y: 0})
+			}
+		}
+
+		bitmap, w, h := ImageToRawBitmap(img)
+		if w != c.w || h != c.h {
+			t.Errorf("expected dimensions %dx%d, got %dx%d", c.w, c.h, w, h)
+		}
+		rowBytes := int(math.Ceil(float64(c.w) / 8.0))
+		want := rowBytes * c.h
+		if len(bitmap) != want {
+			t.Errorf("w=%d h=%d: expected bitmap len %d, got %d", c.w, c.h, want, len(bitmap))
+		}
+	}
+}
+
+// Test 5: PrtQutieDriver.Connect() returns ErrNoDevice (not a panic).
+func TestPrtQutieConnectReturnsErrNoDevice(t *testing.T) {
+	d := NewPrtQutieDriver(9600)
+	err := d.Connect()
+	if err != ErrNoDevice {
+		t.Fatalf("expected ErrNoDevice, got %v", err)
+	}
+}
+
+// Helper: create a dummy file path in temp dir to verify SaveDir is honoured.
+func TestMockDriverSaveDirHonoured(t *testing.T) {
+	dir := t.TempDir()
+	m := NewMockDriver()
+	m.SaveDir = dir
+
+	bitmap := []byte{0xFF, 0xFF} // 2 bytes → 16 pixels wide, 1 row
+	if err := m.Print(bitmap, 16, 1); err != nil {
+		t.Fatalf("Print: %v", err)
+	}
+
+	matches, _ := filepath.Glob(filepath.Join(dir, "hwlab-label-*.png"))
+	if len(matches) == 0 {
+		t.Fatal("no PNG saved in SaveDir")
+	}
+}