when no checkpoints are saved, test fails
Build a model that doesn't save a checkpoint and this crashes.
It should use the last model instead.
model = ...
trainer = Trainer(fast_dev_run)
trainer.fit(model)
trainer.test()

@yukw777
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <torch.serialization._open_file object at 0x7f443d4d88d0>, name = ''
mode = 'rb'

    def __init__(self, name, mode):
>       super(_open_file, self).__init__(open(name, mode))
E       FileNotFoundError: [Errno 2] No such file or directory: ''

The test for this should be:
def test_no_ckpt_test(tmpdir):
    model = EvaluationModel()
    trainer = Trainer(fast_dev_run)
    trainer.fit(model)
    trainer.test()