diff --git a/pyproject.toml b/pyproject.toml
index 592507c..511d36d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -38,3 +38,5 @@ select = ["E", "F", "I", "TID", "UP"]
 # All non-main modules may import from provisioning freely
 "src/planemapper/provision.py" = ["TID251"]
 "src/planemapper/provisioning/*.py" = ["TID251"]
+# Tests may import from provisioning to test its public API
+"tests/provisioning/*.py" = ["TID251"]
diff --git a/tests/provisioning/test_provision_loop.py b/tests/provisioning/test_provision_loop.py
index b8bbd70..a26e65d 100644
--- a/tests/provisioning/test_provision_loop.py
+++ b/tests/provisioning/test_provision_loop.py
@@ -1,2 +1,12 @@
-def test_placeholder() -> None:
-    pass
+from planemapper.provisioning import ProvisioningError
+
+
+def test_provisioning_error_is_exception() -> None:
+    assert issubclass(ProvisioningError, Exception)
+
+
+def test_provisioning_error_can_be_raised_and_caught() -> None:
+    try:
+        raise ProvisioningError("test error")
+    except ProvisioningError as e:
+        assert str(e) == "test error"
diff --git a/tests/test_gpio_ctrl.py b/tests/test_gpio_ctrl.py
index b8bbd70..feda462 100644
--- a/tests/test_gpio_ctrl.py
+++ b/tests/test_gpio_ctrl.py
@@ -1,2 +1,13 @@
-def test_placeholder() -> None:
-    pass
+from planemapper.gpio_ctrl import ButtonHoldDetector, LEDController
+
+
+def test_button_hold_detector_returns_bool() -> None:
+    detector = ButtonHoldDetector()
+    result = detector.check()
+    assert isinstance(result, bool)
+
+
+def test_led_controller_on_off_no_exception() -> None:
+    led = LEDController()
+    led.on()
+    led.off()
diff --git a/tests/test_models.py b/tests/test_models.py
index b8bbd70..4482747 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -1,2 +1,28 @@
-def test_placeholder() -> None:
-    pass
+from planemapper.models import Aircraft
+
+
+def test_aircraft_defaults() -> None:
+    a = Aircraft(icao="ABC123", lat=51.5, lon=-0.1)
+    assert a.heading == 0.0
+    assert a.altitude_ft == 0
+    assert a.callsign == ""
+    assert a.category == ""
+    assert a.is_mlat is False
+    assert a.is_stale is False
+
+
+def test_aircraft_full() -> None:
+    a = Aircraft(
+        icao="ABC123",
+        lat=51.5,
+        lon=-0.1,
+        heading=90.0,
+        altitude_ft=5000,
+        callsign="BAW1",
+        category="A3",
+        is_mlat=True,
+        is_stale=False,
+    )
+    assert a.heading == 90.0
+    assert a.callsign == "BAW1"
+    assert a.is_mlat is True
diff --git a/tests/test_scaffold.py b/tests/test_scaffold.py
new file mode 100644
index 0000000..3ce3da5
--- /dev/null
+++ b/tests/test_scaffold.py
@@ -0,0 +1,84 @@
+import ast
+import importlib.resources
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).parent.parent
+
+
+def test_required_toplevel_modules_exist() -> None:
+    base = REPO_ROOT / "src" / "planemapper"
+    for name in [
+        "__init__.py",
+        "constants.py",
+        "models.py",
+        "main.py",
+        "provision.py",
+        "fetcher.py",
+        "gpio_ctrl.py",
+        "display.py",
+    ]:
+        assert (base / name).exists(), f"Missing: {name}"
+
+
+def test_provisioning_subpackage_exists() -> None:
+    base = REPO_ROOT / "src" / "planemapper" / "provisioning"
+    for name in [
+        "__init__.py",
+        "portal.py",
+        "location.py",
+        "tiles.py",
+        "airspace.py",
+        "wifi.py",
+        "config.py",
+    ]:
+        assert (base / name).exists(), f"Missing provisioning/{name}"
+
+
+def test_renderer_subpackage_exists() -> None:
+    base = REPO_ROOT / "src" / "planemapper" / "renderer"
+    for name in [
+        "__init__.py",
+        "renderer.py",
+        "projection.py",
+        "basemap.py",
+        "aircraft.py",
+        "airspace.py",
+        "colours.py",
+        "icons.py",
+    ]:
+        assert (base / name).exists(), f"Missing renderer/{name}"
+
+
+def test_systemd_units_exist() -> None:
+    systemd = REPO_ROOT / "systemd"
+    assert (systemd / "planemapper-provision.service").exists()
+    assert (systemd / "planemapper-radar.service").exists()
+
+
+def test_airports_csv_via_importlib_resources() -> None:
+    ref = importlib.resources.files("planemapper.data").joinpath("airports.csv")
+    content = ref.read_text(encoding="utf-8")
+    assert len(content) > 0
+    assert "icao_code" in content or "ident" in content  # OurAirports CSV header
+
+
+def test_constants_colours_complete() -> None:
+    from planemapper import constants
+
+    assert len(constants.ALTITUDE_COLOURS) == 6
+    assert len(constants.ALTITUDE_BANDS_FT) == 6
+    assert constants.DISPLAY_WIDTH == 800
+    assert constants.DISPLAY_HEIGHT == 480
+    assert constants.REFRESH_INTERVAL_S == 60
+    assert constants.FETCH_TIMEOUT_S == 5
+
+
+def test_main_does_not_import_provisioning() -> None:
+    main_path = REPO_ROOT / "src" / "planemapper" / "main.py"
+    tree = ast.parse(main_path.read_text())
+    for node in ast.walk(tree):
+        if isinstance(node, (ast.Import, ast.ImportFrom)):
+            if isinstance(node, ast.ImportFrom) and node.module:
+                assert not node.module.startswith("planemapper.provisioning"), (
+                    "main.py must not import from planemapper.provisioning"
+                )