import unittest
from main import start, Task, sleep_forever

async def async_fn():
    pass

class TestAsyncGui(unittest.TestCase):

    def test__unsupported_type(self):
        func = lambda: None
        gen = (i for i in range(3))

        for v in (func, gen):
            with self.assertRaises(ValueError):
                start(v)

    def test__return_value_is_a_Task(self):
        for v in [Task(sleep_forever()), sleep_forever(), async_fn()]:
            r = start(v)
            self.assertIsInstance(r, Task)

    def test__already_started(self):
        task1 = start(sleep_forever())
        task2 = start(async_fn())
        
        for task in (task1, task2):
            with self.assertRaises(ValueError):
                start(task)

if __name__ == '__main__':
    unittest.main()