Add more unit tests

I'm now testing camera metadata and stage functionality. This is only using
the simulated HW - but it's a start.

It would be good to add tests for the
camera-stage mapping Thing, though
that may require speeding up the stage.

tests/test_dummy_server.py

@@ -1,9 +1,11 @@
+import json
 import tempfile
 
 from fastapi import Depends, FastAPI
 from fastapi.testclient import TestClient
-
 from labthings_fastapi.client import ThingClient
+from PIL import Image
+import piexif
 
 from openflexure_microscope_server.server import ThingServer
 from openflexure_microscope_server.things.camera.simulation import SimulatedCamera
@@ -20,3 +22,33 @@ def test_autofocus():
     with TestClient(server.app) as client:
         autofocus = ThingClient.from_url("/autofocus/", client)
         _ = autofocus.fast_autofocus()
+
+def test_grab_jpeg():
+    with TestClient(server.app) as client:
+        camera = ThingClient.from_url("/camera/", client)
+        blob = camera.grab_jpeg()
+        _image = Image.open(blob.open())
+
+def test_capture_jpeg_metadata():
+    with TestClient(server.app) as client:
+        camera = ThingClient.from_url("/camera/", client)
+        blob = camera.capture_jpeg()
+        image = Image.open(blob.open())
+        exif_dict = piexif.load(image.info["exif"])
+        encoded_metadata = exif_dict["Exif"][piexif.ExifIFD.UserComment]
+        metadata = json.loads(encoded_metadata)
+        assert "position" in metadata["/stage/"]
+
+def test_stage():
+    with TestClient(server.app) as client:
+        stage = ThingClient.from_url("/stage/", client)
+        start = stage.position
+        move = {"x": 1, "y": 2, "z": 3}
+        stage.move_relative(**move)
+        pos = stage.position
+        for s, m, p in zip(start.values(), move.values(), pos.values()):
+            assert s + m == p
+        stage.move_relative(**{k: -v for k, v in move.items()})
+        pos = stage.position
+        for s, p in zip(start.values(), pos.values()):
+            assert s == p