def METHOD_NAME(self):
    """Test that the vlans() method behaves correctly"""
    vlan100 = MockVLAN("v100")
    vlan200 = MockVLAN("v200")
    vlan300 = MockVLAN("v300")
    tagged_vlans = [vlan200, vlan300]
    native_vlan = vlan100
    port = Port(1, 1, {})
    port.native_vlan = native_vlan
    self.assertIn(native_vlan, port.vlans())
    port.tagged_vlans = tagged_vlans
    self.assertEqual(set(port.vlans()), set([native_vlan] + tagged_vlans))
    port.native_vlan = None
    self.assertEqual(set(port.vlans()), set(tagged_vlans))