add test for trainer.test()

[Varal7]

Fixes #1857

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What does this PR do?

Fixes #1857.

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[williamFalcon]

can you add a test for this? this is great!

[awaelchli]

see also #1804, is it not the same?

[pep8speaks]

Hello @Varal7! Thanks for updating this PR.

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2020-05-17 15:02:52 UTC

[Varal7]

Indeed there seems to be work ongoing in #1804, #1720, #1754, #1804 already.

I wrote a test case just in case.

[williamFalcon]

@Varal7 can you rebase with master and double check that this works?

The test is still useful!