def get_previous_release(current_release):
""" Return the previously active release from the history file """
releases = list_releases()
try:
current_index = last_index(releases, current_release)
previous_index = current_index - 1
if previous_index < 0:
return None
else:
return releases[previous_index]
except ValueError:
# raised if the current release is not found
return None
def test_last_index_empty():
with pytest.raises(ValueError):
last_index([], 1)
def test_last_index():
assert last_index([1, 1], 1) == 1
assert last_index([1, 1, 2], 1) == 1
def test_last_index_missing():
with pytest.raises(ValueError):
last_index([1], 2)