def test_lookup_from_inner_env():
"""The `extend` function returns a new environment extended with more bindings."""
env = Environment({"foo": 42})
env = env.extend({"bar": True})
assert_equals(42, env.lookup("foo"))
assert_equals(True, env.lookup("bar"))
def test_extend_returns_new_environment():
"""The extend method should create a new environment, leaving the old one unchanged."""
env = Environment({"foo": 1})
extended = env.extend({"foo": 2})
assert_equals(1, env.lookup("foo"))
assert_equals(2, extended.lookup("foo"))