make hardware emulation reversible

fixes an issue that can be caused by side effects of certain tests

src/raspi_poe_mon/mock.py

@@ -10,11 +10,32 @@
 logger = logging.getLogger('raspi_poe_mon')
 
 
-def monkeypatch():
-    """monkeypatch all real hardware so the mock version is used instead. restart to undo"""
-    serial.i2c = MockFan
-    device.ssd1306 = MockDisplay
-    render.canvas = MockCanvas
+class HardwarePatcher:
+    """allows to monkeypatch all real hardware so the mock versions are used instead"""
+
+    real_i2c = serial.i2c
+    real_ssd1306 = device.ssd1306
+    real_canvas = render.canvas
+
+    @classmethod
+    def patch(cls):
+        serial.i2c = MockFan
+        device.ssd1306 = MockDisplay
+        render.canvas = MockCanvas
+
+    @classmethod
+    def restore(cls):
+        serial.i2c = cls.real_i2c
+        device.ssd1306 = cls.real_ssd1306
+        render.canvas = cls.real_canvas
+
+    @classmethod
+    def is_real(cls) -> bool:
+        return (
+            serial.i2c == cls.real_i2c
+            and device.ssd1306 == cls.real_ssd1306
+            and render.canvas == cls.real_canvas
+        )
 
 
 class MockDisplay:

src/raspi_poe_mon/poe_hat.py

@@ -6,7 +6,7 @@
 from luma.oled import device
 from PIL.ImageDraw import ImageDraw
 
-from raspi_poe_mon import mock
+from raspi_poe_mon.mock import HardwarePatcher
 
 
 class PoeHat:
@@ -25,7 +25,7 @@ def __init__(self, dry_run=False, brightness=100) -> None:
         self.display: Optional[device.ssd1306] = None
         self.fan_state = False
         if self.dry_run:
-            mock.monkeypatch()
+            HardwarePatcher.patch()
 
     def fan_connect(self, force=False):
         if force or self.i2c_fan is None:
@@ -69,3 +69,5 @@ def draw(self) -> ImageDraw:
     def cleanup(self):
         self.fan_off()
         self.display_clear()
+        if self.dry_run:
+            HardwarePatcher.restore()

tests/test_cli.py

@@ -4,6 +4,7 @@
 
 from raspi_poe_mon import main
 from raspi_poe_mon.main import app
+from raspi_poe_mon.mock import HardwarePatcher
 from raspi_poe_mon.version import __version__
 
 runner = CliRunner()
@@ -43,9 +44,13 @@ def validate_help(result: Result, contains: str):
 
 @pytest.mark.timeout(2)
 def test_dry_run():
+    assert HardwarePatcher.is_real()
     main.run(dry_run=True, verbose=True, frame_time=0.02, timeout=0.05)
+    assert HardwarePatcher.is_real()
 
 
 @pytest.mark.timeout(2)
 def test_profiling():
+    assert HardwarePatcher.is_real()
     main.run(dry_run=True, profiling=True, frame_time=0.05, timeout=0.1)
+    assert HardwarePatcher.is_real()

tests/test_mock.py

@@ -0,0 +1,9 @@
+from raspi_poe_mon.mock import HardwarePatcher
+
+
+def test_hardware_patcher():
+    assert HardwarePatcher.is_real() is True
+    HardwarePatcher.patch()
+    assert HardwarePatcher.is_real() is False
+    HardwarePatcher.restore()
+    assert HardwarePatcher.is_real() is True