diff --git a/src/openflexure_microscope_server/things/__init__.py b/src/openflexure_microscope_server/things/__init__.py
index c497209f..255e0379 100644
--- a/src/openflexure_microscope_server/things/__init__.py
+++ b/src/openflexure_microscope_server/things/__init__.py
@@ -5,6 +5,7 @@ with other Things and including them in the LabThings-FastAPI config file.
 """
 
 import os
+from types import TracebackType
 from typing import Optional, Self
 
 import labthings_fastapi as lt
@@ -35,6 +36,19 @@ class OFMThing(lt.Thing):
         )
         return self
 
+    def __exit__(
+        self,
+        _exc_type: type[BaseException],
+        _exc_value: Optional[BaseException],
+        _traceback: Optional[TracebackType],
+    ) -> None:
+        """Close the OFMThing.
+
+        This is needed for the context manager protocol to work. Currently it doesn't
+        do anything.
+        """
+        pass
+
     @property
     def data_dir(self) -> str:
         """The data directory for this thing."""
diff --git a/src/openflexure_microscope_server/things/stage_measure.py b/src/openflexure_microscope_server/things/stage_measure.py
index c9422072..cedfaa0f 100644
--- a/src/openflexure_microscope_server/things/stage_measure.py
+++ b/src/openflexure_microscope_server/things/stage_measure.py
@@ -202,11 +202,7 @@ class RangeofMotionThing(OFMThing):
 
             timestamp = datetime.now().strftime("%Y_%m_%d_%H_%M")
             datafile_path = os.path.join(self.data_dir, f"rom_data_{timestamp}.json")
-            with open(
-                datafile_path,
-                "w",
-                encoding="utf-8",
-            ) as f:
+            with open(datafile_path, "w", encoding="utf-8") as f:
                 json.dump(data, f, indent=4)
 
         finally:
diff --git a/tests/unit_tests/test_stage_measure.py b/tests/unit_tests/test_stage_measure.py
index fad2df21..9204878f 100644
--- a/tests/unit_tests/test_stage_measure.py
+++ b/tests/unit_tests/test_stage_measure.py
@@ -1,6 +1,7 @@
 """File contains unit tests for stage_measure."""
 
 import logging
+import tempfile
 from copy import copy
 
 import numpy as np
@@ -148,11 +149,14 @@ def test_error_if_no_stream_res_set_when_requesting_img_coords():
 
 
 @pytest.fixture
-def rom_thing(example_rom_data, csm_matrix) -> stage_measure.RangeofMotionThing:
+def rom_thing(example_rom_data, csm_matrix, mocker) -> stage_measure.RangeofMotionThing:
     """Yield a RangeofMotionThing already populated with some example rom_data."""
     rom_thing = create_thing_without_server(
         stage_measure.RangeofMotionThing, mock_all_slots=True
     )
+    type(rom_thing._thing_server_interface).application_config = mocker.PropertyMock(
+        return_value={"data_folder": tempfile.gettempdir()}
+    )
     rom_thing._stream_resolution = [800, 600]
     rom_thing._rom_data = example_rom_data
 
@@ -586,7 +590,7 @@ def test_perform_rom_actions_locked(rom_thing):
         rom_thing.perform_recentre()
 
 
-def test_perform_rom_test_(rom_thing, mocker):
+def test_perform_rom_test(rom_thing, mocker):
     """Check that perform Rom Test runs the expected high level algorithm."""
 
     def check_and_modify_rom_data(axis: str, direction: int, **_kwargs):
@@ -605,7 +609,10 @@ def test_perform_rom_test_(rom_thing, mocker):
     mocker.patch.object(
         rom_thing._cam, "grab_as_array", return_value=np.zeros([123, 456, 3])
     )
-    final_dict = rom_thing.perform_rom_test()
+
+    # Enter the ROM thing to get the data directory.
+    with rom_thing as running_rom_thing:
+        final_dict = running_rom_thing.perform_rom_test()
 
     # This should take less than 1 sec
     assert final_dict["Time"] <= 1