def test_a_rule_depends_on_its_stock(self):
rule = PriceRule("MSFT", lambda stock: stock.price > 10)
assert rule.depends_on() == "MSFT"
def test_a_PriceRule_only_depends_on_its_stock(self):
"""Tests if a PriceRule only depends on its stock"""
rule = PriceRule("MSFT", lambda stock: stock.price > 10)
self.assertEqual({"MSFT"}, rule.depends_on())
