test: add async fetch coverage for TimeWindow data source

[LeSingh1]

Summary

Adds focused async coverage for TimeWindow.fetch().

This verifies that async fetch:

• applies time offsets
• preserves output time coordinates
• returns variables in the expected order

Closes #589.

Test plan

• python -m pytest test/data/test_time_window.py -v

Result: 28 passed, 1 skipped.

[greptile-apps]

Greptile Summary

Adds async coverage for TimeWindow.fetch() by introducing a fetch coroutine on MockDataSource and one new test that verifies variable ordering, time-coordinate preservation, and offset application through the async path.

• MockDataSource.fetch delegates to __call__, so existing call-history tracking works transparently for the new test.
• The new test uses asyncio.run() rather than the @pytest.mark.asyncio / async def pattern used everywhere else in the repo, and it only asserts the first of the three offset calls, leaving the 0 h and +6 h paths unverified.

Confidence Score: 4/5

Test-only change; no production code is modified and the new test exercises a real code path.

The test uses asyncio.run() rather than the project's established @pytest.mark.asyncio pattern, and verifies only one of three offset calculations, leaving a gap in the coverage it claims to provide.

test/data/test_time_window.py — async test style and incomplete offset assertions.

Important Files Changed

Filename	Overview
test/data/test_time_window.py	Adds async def fetch to MockDataSource and one new test covering async variable ordering and time-coordinate alignment; uses asyncio.run() instead of the project's standard @pytest.mark.asyncio pattern, and only asserts the first of three offset calls.

_{Reviews (1): Last reviewed commit: "test: add async fetch coverage for TimeW..." | Re-trigger Greptile}

[greptile-apps]

The project is configured with pytest-asyncio (asyncio_mode = "strict") and all other async tests in this repo use @pytest.mark.asyncio with async def (see test_data_utils.py, test_async_zarr.py, test_server_utils.py). Using asyncio.run() in a sync wrapper diverges from that established convention, and calling asyncio.run() from within a running event loop (e.g. if an async fixture or plugin attaches one) will raise RuntimeError: This event loop is already running.

Suggested change

	def test_fetch_matches_sync_output_coordinates(self):
	"""Test async fetch applies offsets and preserves output coordinates."""
	ds = MockDataSource()
	tw = TimeWindow(
	datasource=ds,
	offsets=[timedelta(hours=-6), timedelta(hours=0), timedelta(hours=6)],
	suffixes=["_tm1", "_t", "_tp1"],
	)
	base_time = datetime(2024, 1, 1, 12, 0)
	result = asyncio.run(tw.fetch(base_time, ["t2m", "u10m"]))
	@pytest.mark.asyncio
	async def test_fetch_matches_sync_output_coordinates(self):
	"""Test async fetch applies offsets and preserves output coordinates."""
	ds = MockDataSource()
	tw = TimeWindow(
	datasource=ds,
	offsets=[timedelta(hours=-6), timedelta(hours=0), timedelta(hours=6)],
	suffixes=["_tm1", "_t", "_tp1"],
	)
	base_time = datetime(2024, 1, 1, 12, 0)
	result = await tw.fetch(base_time, ["t2m", "u10m"])

[greptile-apps]

Only the first offset call (-6 h) is verified. The corresponding sync test test_offset_times_calculated_correctly checks all three call-history entries. Without checking indices 1 (0 h → 12:00) and 2 (+6 h → 18:00) the test could pass even if the offset arithmetic for the later calls was broken.

Suggested change

	assert actual_vars == expected_vars
	assert result.time.values[0] == np.datetime64(base_time)
	assert ds.call_history[0]["time"] == [datetime(2024, 1, 1, 6, 0)]
	assert actual_vars == expected_vars
	assert result.time.values[0] == np.datetime64(base_time)
	assert ds.call_history[0]["time"] == [datetime(2024, 1, 1, 6, 0)] # -6h
	assert ds.call_history[1]["time"] == [datetime(2024, 1, 1, 12, 0)] # 0h
	assert ds.call_history[2]["time"] == [datetime(2024, 1, 1, 18, 0)] # +6h