Adding test helper functions

I thought these two functions might help reduce duplication in our tests since we seem to be performing the same logic over and over again. This PR is just a RFC, so if it's something we want, I'll go ahead and update our tests to use it :smile: 
Maybe this shouldn't always be a `t.Fatalf`? Sometimes you want a `t.Errorf` and sometimes you want a `t.Fatalf`. Maybe two sets of functions: `AssertEquals` that's fatal if it fails, and `CheckEquals` that isn't?