diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..7a7e3f4
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,25 @@
+name: Tests
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+    branches: [main, master]
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ['3.11', '3.12']
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install pytest
+          if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+      - name: Run tests
+        run: python -m pytest tests/ -v
diff --git a/tests/test_pidslm.py b/tests/test_pidslm.py
new file mode 100644
index 0000000..1e18f0a
--- /dev/null
+++ b/tests/test_pidslm.py
@@ -0,0 +1,247 @@
+"""Tests for piDSLM - Raspberry Pi DSLR Camera Controller"""
+
+import pytest
+from unittest.mock import patch, MagicMock
+import os
+import glob
+
+
+def test_timestamp_generates_valid_format(source_module):
+    """Test that timestamp method generates a valid datetime string format."""
+    app = source_module.piDSLM()
+    # Mock the datetime to have predictable output
+    with patch('pidslm.datetime') as mock_datetime:
+        mock_datetime.datetime.now.return_value.strftime.return_value = "20231201_120000"
+        result = app.timestamp()
+        assert result == "20231201_120000"
+        assert len(result) == 15  # YYYYMMDD_HHMMSS format is 15 chars
+
+
+def test_clear_removes_files(source_module, tmp_path, monkeypatch):
+    """Test that clear method removes files from Downloads folder."""
+    app = source_module.piDSLM()
+    
+    # Mock the Downloads directory
+    downloads_dir = str(tmp_path)
+    
+    # Create some test files
+    test_file = tmp_path / "test.jpg"
+    test_file.write_text("test content")
+    
+    # Patch os.system to capture commands
+    with patch('pidslm.os.system') as mock_system:
+        app.clear()
+        # Verify the rm command was called
+        mock_system.assert_called_once()
+        assert "rm -v" in mock_system.call_args[0][0]
+
+
+def test_show_busy_displays_window(source_module):
+    """Test that show_busy method displays the busy window."""
+    app = source_module.piDSLM()
+    
+    # Mock the busy window show method
+    with patch.object(app.busy, 'show') as mock_show:
+        app.show_busy()
+        mock_show.assert_called_once()
+
+
+def test_hide_busy_hides_window(source_module):
+    """Test that hide_busy method hides the busy window."""
+    app = source_module.piDSLM()
+    
+    # Mock the busy window hide method
+    with patch.object(app.busy, 'hide') as mock_hide:
+        app.hide_busy()
+        mock_hide.assert_called_once()
+
+
+def test_burst_capture(source_module):
+    """Test burst capture functionality."""
+    app = source_module.piDSLM()
+    
+    with patch('pidslm.os.system') as mock_system:
+        with patch.object(app, 'show_busy'):
+            with patch.object(app, 'hide_busy'):
+                app.burst()
+                mock_system.assert_called_once()
+                assert "raspistill" in mock_system.call_args[0][0]
+                assert "-tl 0" in mock_system.call_args[0][0]
+                assert "-bm" in mock_system.call_args[0][0]
+
+
+def test_video_capture(source_module):
+    """Test video capture functionality."""
+    app = source_module.piDSLM()
+    
+    with patch('pidslm.os.system') as mock_system:
+        with patch.object(app, 'show_busy'):
+            with patch.object(app, 'hide_busy'):
+                app.video_capture()
+                mock_system.assert_called_once()
+                assert "raspivid" in mock_system.call_args[0][0]
+                assert "-t 30000" in mock_system.call_args[0][0]
+
+
+def test_split_hd_30m_capture(source_module):
+    """Test 30-minute split HD video capture."""
+    app = source_module.piDSLM()
+    
+    with patch('pidslm.os.system') as mock_system:
+        with patch.object(app, 'show_busy'):
+            with patch.object(app, 'hide_busy'):
+                app.split_hd_30m()
+                mock_system.assert_called_once()
+                assert "raspivid" in mock_system.call_args[0][0]
+                assert "-t 1800000" in mock_system.call_args[0][0]
+                assert "-sg 300000" in mock_system.call_args[0][0]
+
+
+def test_lapse_capture(source_module):
+    """Test time-lapse capture functionality."""
+    app = source_module.piDSLM()
+    
+    with patch('pidslm.os.system') as mock_system:
+        with patch.object(app, 'show_busy'):
+            with patch.object(app, 'hide_busy'):
+                app.lapse()
+                mock_system.assert_called_once()
+                assert "raspistill" in mock_system.call_args[0][0]
+                assert "-t 3600000" in mock_system.call_args[0][0]
+                assert "-tl 60000" in mock_system.call_args[0][0]
+
+
+def test_long_preview(source_module):
+    """Test long preview functionality."""
+    app = source_module.piDSLM()
+    
+    with patch('pidslm.os.system') as mock_system:
+        with patch.object(app, 'show_busy'):
+            with patch.object(app, 'hide_busy'):
+                app.long_preview()
+                mock_system.assert_called_once()
+                assert "raspistill" in mock_system.call_args[0][0]
+                assert "-t 15000" in mock_system.call_args[0][0]
+
+
+def test_capture_image(source_module):
+    """Test single image capture functionality."""
+    app = source_module.piDSLM()
+    
+    with patch('pidslm.os.system') as mock_system:
+        with patch.object(app, 'show_busy'):
+            with patch.object(app, 'hide_busy'):
+                app.capture_image()
+                mock_system.assert_called_once()
+                assert "raspistill" in mock_system.call_args[0][0]
+
+
+def test_upload_calls_dropbox_script(source_module):
+    """Test Dropbox upload functionality."""
+    app = source_module.piDSLM()
+    
+    with patch('pidslm.subprocess.Popen') as mock_popen:
+        with patch.object(app, 'show_busy'):
+            with patch.object(app, 'hide_busy'):
+                app.upload()
+                mock_popen.assert_called_once()
+                call_args = mock_popen.call_args[0][0]
+                # call_args is a list like ['python3', '/home/pi/piDSLM/dropbox_upload.py', '--yes']
+                assert any("dropbox_upload.py" in arg for arg in call_args)
+                assert any("--yes" in arg for arg in call_args)
+
+
+def test_fullscreen_mode(source_module):
+    """Test fullscreen mode functionality."""
+    app = source_module.piDSLM()
+    
+    with patch.object(app.app.tk, 'attributes') as mock_attrs:
+        app.fullscreen()
+        mock_attrs.assert_called_once_with("-fullscreen", True)
+
+
+def test_not_fullscreen_mode(source_module):
+    """Test non-fullscreen mode functionality."""
+    app = source_module.piDSLM()
+    
+    with patch.object(app.app.tk, 'attributes') as mock_attrs:
+        app.notfullscreen()
+        mock_attrs.assert_called_once_with("-fullscreen", False)
+
+
+def test_show_gallery(source_module):
+    """Test gallery display functionality."""
+    app = source_module.piDSLM()
+    
+    # Mock glob to return a list with one test image
+    test_image = "/home/pi/Downloads/test.jpg"
+    with patch('pidslm.glob.glob', return_value=[test_image]):
+        with patch('pidslm.Window') as mock_window:
+            with patch('pidslm.PushButton'):
+                with patch('pidslm.Picture'):
+                    app.show_gallery()
+                    # Gallery window should be created
+                    assert hasattr(app, 'gallery')
+
+
+def test_gpio_setup(source_module):
+    """Test GPIO pin setup during initialization."""
+    with patch('pidslm.GPIO') as mock_gpio:
+        app = source_module.piDSLM()
+        
+        # Verify GPIO setup was called
+        mock_gpio.setwarnings.assert_called_once_with(False)
+        mock_gpio.setmode.assert_called_once_with(mock_gpio.BCM)
+        # GPIO.setup should be called at least once (for button pin)
+        assert mock_gpio.setup.called
+        # Check that GPIO 16 was set up as input with pull-up
+        call_args = mock_gpio.setup.call_args
+        # call_args is a tuple of (args, kwargs)
+        args = call_args[0] if call_args else ()
+        kwargs = call_args[1] if len(call_args) > 1 else {}
+        assert args[0] == 16
+        assert args[1] == mock_gpio.IN
+        assert kwargs.get('pull_up_down') == mock_gpio.PUD_UP
+
+
+def test_take_picture_callback(source_module):
+    """Test the takePicture callback function."""
+    app = source_module.piDSLM()
+    
+    with patch('pidslm.os.system') as mock_system:
+        # Simulate button press callback
+        app.takePicture(16)
+        mock_system.assert_called_once()
+        assert "raspistill" in mock_system.call_args[0][0]
+        assert "-t 3500" in mock_system.call_args[0][0]
+
+
+def test_saved_pictures_list(source_module):
+    """Test that saved_pictures list is initialized correctly."""
+    app = source_module.piDSLM()
+    assert isinstance(app.saved_pictures, list)
+    assert len(app.saved_pictures) == 0
+
+
+def test_picture_index_initialization(source_module):
+    """Test that picture_index is initialized to 0."""
+    app = source_module.piDSLM()
+    assert app.picture_index == 0
+
+
+def test_capture_number_initialization(source_module):
+    """Test that capture_number is initialized with timestamp."""
+    app = source_module.piDSLM()
+    assert app.capture_number == app.timestamp()
+
+
+def test_video_capture_number_initialization(source_module):
+    """Test that video_capture_number is initialized with timestamp."""
+    app = source_module.piDSLM()
+    assert app.video_capture_number == app.timestamp()
+
+
+def test_shown_picture_initialization(source_module):
+    """Test that shown_picture is initialized to empty string."""
+    app = source_module.piDSLM()
+    assert app.shown_picture == ""