def test_expiration():
time = 1
cache = Cache(max_age=5, clock=lambda:time)
# Ensure that the clock value is coming from the current value of the
# `time` variable.
assert cache.clock() == 1
time = 2
assert cache.clock() == 2
cache['a'] = 'b'
cache['b'] = 'c'
time += 3
cache['c'] = 'd'
cache['d'] = 'e'
assert len(cache) == 4
assert len(cache.queue) == 4
cache.evict_expired()
assert len(cache) == 4
assert len(cache.queue) == 4
time += 3
cache.evict_expired()
assert len(cache) == 2
assert len(cache.queue) == 2
assert 'a' not in cache
assert 'b' not in cache
assert 'c' in cache
assert 'd' in cache
cache['c'] = 'f'
assert len(cache) == 2
assert len(cache.queue) == 3
time += 3
cache.evict_expired()
assert len(cache) == 1
assert len(cache.queue) == 1
assert 'c' in cache
try:
_ = cache['d']
assert False, "'d' should not be in cache"
except IndexError:
pass
