coroutines that return before their first yield cause the simulator to shutdown

Repro:

@cocotb.test()
def test_func_empty(dut):
    """ Test that a function can complete before the first yield """
    @cocotb.coroutine
    def func_empty():
        print("This line runs")
        return
        yield  # needed to make this a coroutine
    yield func_empty()
    print("This line is never reached")

[marlonjames]

If I remove all of the clk_gen = cocotb.fork(Clock(dut.clk, 100).start()) lines and run the test_external module on #1705, everything passes.

[eric-wieser]

It looks to me like test_ext_exit_error is just nonsense - I’d remove it as part of the cleanup.