def test_keys(cache):
    'Retrieve keys of items in cache.'
    assert (cache.keys() == [])
    cache.set('a', 'a_value')
    cache.set('b', 'b_value')
    cache.set('c', 'c_value')
    assert (sorted(cache.keys()) == sorted(['a', 'b', 'c']))
Retrieve keys of items in cache.
def test_keys(cache):
    
    assert (cache.keys() == [])
    cache.set('a', 'a_value')
    cache.set('b', 'b_value')
    cache.set('c', 'c_value')
    assert (sorted(cache.keys()) == sorted(['a', 'b', 'c']))