Fix truncated diagnostics in go-cmp diffs in tests

[paddycarver]

We use go-cmp pretty extensively in our tests to compare values. This works great, except when comparing diagnostics. As documented in google/go-cmp#279, our diagnostic detail output usually gets truncated, mostly right after telling us that an error occurred and it's always a problem with the provider. This leads to us littering logging statements around logging error output in our tests, which feels suboptimal.

I think we can write a customer Reporter but that seems like a large-ish undertaking, requires us to pass an option to all our calls to cmp.Diff, and I'm confused about whether we can use that for Diff or if it's just for Equal.

Seeing how google/go-cmp#279 resolves may help guide what we want to do here.

[bflad]

Now tracking upstream at google/go-cmp#264

[bflad]

A unit testing workaround is looping through diagnostics with t.Logf() with something like:

if diff := cmp.Diff(resp.Diagnostics, testCase.expectedDiagnostics); diff != "" {
  for _, diagnostic := range resp.Diagnostics {
    t.Logf("unexpected diagnostic: %s", diagnostic)
  }
  t.Fatalf("unexpected diagnostics difference: %s", diff)
}

While we could say this is the desired implementation until there is further clarity on go-cmp changes or recommendations, this is hard to "enforce" so it is generally used as a temporary unit test troubleshooting step, rather than inconsistently implemented across the various unit testing.

[bflad]

We're still waiting on google/go-cmp#264 upstream for this and trying to pare down the issue tracker to actionable items, for reasons. Let's stay subscribed upstream and use the t.Logf() workaround for now until someone has some time to investigate further.

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