Add test for tetramm frame time

Author: DiamondJoseph

src/dodal/devices/areadetector/adaravis.py

@@ -143,7 +143,7 @@ class AdAravisMakoController(DetectorControl):
     # TODO: Extract this to config and actually use the model of the camera.
     # https://github.com/DiamondLightSource/dodal/issues/340
     # cite: https://cdn.alliedvision.com/fileadmin/content/documents/products/cameras/various/appnote/GigE/GigE-Cameras_AppNote_PIV-Min-Time-Between-Exposures.pdf
-    deadtime_map: Dict[str, float] = {
+    _deadtime_map: Dict[str, float] = {
         "GB650": 78.0e-6,
         "GC650": 121e-6,
         "GE680": 38.2e-6,
@@ -240,7 +240,7 @@ def __init__(self, driver: AdAravisMakoDriver, gpio_number: int) -> None:
 
     def get_deadtime(self, exposure: float) -> float:
         # https://github.com/DiamondLightSource/dodal/issues/340
-        return self.deadtime_map.get("G-234")
+        return self._deadtime_map.get("G-234")
 
     async def arm(
         self,

tests/devices/unit_tests/test_tetramm.py

@@ -68,3 +68,22 @@ async def test_excepts_for_invalid_triggers(tetramm_controller: TetrammControlle
         await tetramm_controller.arm(DetectorTrigger.internal)
     # Function excepts early and does not do any sets
     assert tetramm_controller._drv.averaging_time == previous_averaging_time
+
+
+async def test_set_frame_time(tetramm_controller: TetrammController):
+    """
+    frame_time >= readings_per_frame * values_per_reading / sample_rate
+    With the default values:
+    base_sample_rate = 100_000
+    minimum_values_per_reading = 5
+    readings_per_frame = 1_000
+    frame_time >= 1_000 * 5 / 100_000 = 1/20
+    """
+
+    await tetramm_controller.set_frame_time(1 / 19)
+
+    with pytest.raises(
+        ValueError,
+        match="frame_time 0.02 is too low to collect at least 5 values per reading, at 1,000 readings per frame.",
+    ):
+        await tetramm_controller.set_frame_time(1 / 50)