Add export and validation handler tests

[akchinSTC]

Partially addresses #747

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[kiersten-stokes]

The _async_return functionality is cool! Other than that, yeah I think these tests pretty much cover what we want them to. My only NIT is that the comments could probably be cleaned up/edited a bit (though I know why they are as they are right now 🙂 )

[kiersten-stokes]

LGTM!