In retrospect, silently returning nothing when the user switches the start and end dates seems like poor behavior and we should warn them that they are making a malformed request. We would typically do that by raising an exception.
Modify the build_asos_request_url function to raise an error when the dates
are switched (put right above string building):
# Make sure the starting and ending dates are not reversed
if start_date > end_date:
raise ValueError('Start date cannot be after end date.')
Now we need to change our test to verify that the ValueError is raised. Don’t
forget to remove the now unused fixture.
def test_download_asos_data_start_after_end():
"""Test for correct behavior when start and end times are reversed."""
# Setup
start = datetime.datetime(2018, 8, 1, 12)
end = datetime.datetime(2018, 7, 1, 12)
# Exercise/Verify
with pytest.raises(ValueError):
meteogram.build_asos_request_url('AMW', start, end)
# Cleanup - none necessary