Broaden test so that it writes the CSV file out

tests/test_file_writer.py

@@ -1,6 +1,10 @@
+import os
+
 import pytest
-from src.csv_writer import create_file_name
+
+from src import csv_writer
 from datetime import datetime, timezone
+import locations
 
 
 @pytest.mark.parametrize(
@@ -13,15 +17,33 @@
     ],
 )
 def test_create_file_name_handles_units(
-    units, variable_id, channel_id, expected_filename, tmp_path
+    monkeypatch, units, variable_id, channel_id, expected_filename, tmp_path
 ):
-    observationTime = datetime(2025, 1, 1, 10, 10, 10, tzinfo=timezone.utc)
-    csn = "12345678"
+    # treat the normal absolute path as if it were a relative path, so we can put
+    # a prefix on it (this code is usually run in a container)
+    original_csv_dir = tmp_path / locations.WAVEFORM_ORIGINAL_CSV.relative_to("/")
+    monkeypatch.setattr(csv_writer, "WAVEFORM_ORIGINAL_CSV", original_csv_dir)
+    monkeypatch.setattr(locations, "WAVEFORM_ORIGINAL_CSV", original_csv_dir)
 
-    filename = create_file_name(variable_id, channel_id, observationTime, csn, units)
+    # the only precondition is that the base dir must exist
+    original_csv_dir.parent.mkdir(parents=True, exist_ok=True)
+
+    observation_time = datetime(2025, 1, 1, 10, 10, 10, tzinfo=timezone.utc)
+    csn = "12345678"
+    mrn = "whatever"
 
-    assert filename == expected_filename
+    csv_writer.write_frame(
+        {"value": "[1,2,3]"},
+        variable_id,
+        channel_id,
+        observation_time.timestamp(),
+        units,
+        50,
+        "mapped loc",
+        csn,
+        mrn,
+    )
 
-    # check we can write to it
-    with open(f"{tmp_path}/{filename}", "w") as fileout:
-        fileout.write("Test string")
+    # check that we can find the data again in its expected place
+    expected_csv_path = locations.WAVEFORM_ORIGINAL_CSV / expected_filename
+    assert os.path.exists(expected_csv_path)