Stronger --checkpoint-activations test (#1505)
Stronger --checkpoint-activations test (#1505)

Summary:
- captures and inspects train and valid logs using unittest's `assert_logs_equal`
- asserts that `--checkpoint-activations` does not change `train_loss` or `valid_loss`.

Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/1505

Reviewed By: myleott

Differential Revision: D25544991

Pulled By: sshleifer

fbshipit-source-id: 2762095ab4e7c819a803b3556f5774db8c6b6f39

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq