def test_write_layered_source():
source1 = DictSource({'a': 1, 'b': {'c': 2}})
source2 = DictSource({'x': 6, 'b': {'y': 7, 'd': {'e': 8}}})
config = LayeredConfig(source1, source2)
assert config.a == 1
assert config.b.c == 2
assert config.b.y == 7
config.a = 10
config['x'] = 60
config['b'].c = 20
config.b['y'] = 70
config.b['m'] = 'n' # add new key
config.b.d.e = 80
assert config.a == 10
assert config.x == 60
assert config.b.c == 20
assert config.b.y == 70
assert config.b.m == 'n'
assert config.b.d.e == 80
assert source1.a == 10
assert source1.b.c == 20
assert source2.x == 60
assert source2.b.y == 70
assert source2.b.m == 'n'
assert source2.b.d.e == 80
