zaptest: Expand TestingT interface

[abhinav]

This expands the TestingT interface to a much larger subset of
testing.TB.

The following were left out:

• Error and Log were left out in favor of Errorf and Logf
• Fatal* methods were left out in favor of Errorf followed by
  FailNow
• Skip* methods were left out because our test logger shouldn't be
  skipping tests
• Helper was left out because not all supported verisons of Go have
  that

I'm putting this in a separate PR so that we can discuss every included/omitted
method outside #518.

CC @akshayjshah @prashantv

[codecov]

Codecov Report

Merging #565 into abg/test-logger will not change coverage.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           abg/test-logger     #565   +/-   ##
================================================
  Coverage            97.48%   97.48%           
================================================
  Files                   40       40           
  Lines                 2026     2026           
================================================
  Hits                  1975     1975           
  Misses                  43       43           
  Partials                 8        8

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[prashantv]

do we need Fail when we already have Logf and Errorf?

[abhinav]

Fail marks the test as having failed without logging a message.
Errorf("") will still emit an empty string.

We don't necessarily need this but I can see its value if you want to log a
multi-line complex message before you mark the test as failed.

[prashantv]

I'm OK either way, if we have use-cases where we want to log a message separately to using Errorf, then we can keep it. If we haven't done this in our other projects, then perhaps we don't need it.

[abhinav]

How we mark tests as failed in normal tests in other projects isn't
that important here. This interface controls which methods are
available to our testing utility. If we decide to add more features to
the test logger in the future, it'll be difficult to request more of
the methods from testing.TB.

The intent here is to get the minimal standalone functionality of
testing.TB. I wouldn't mind dropping Errorf in favor of just Logf and
Fail but we want Errorf for testify compatibility.

FWIW, we are using Fail in the logger returned by zaptest.NewLogger:
We use it when the SyncWriter needs to mark the test as failed if
anything gets written to ErrorOutput. (#566)

[abhinav]

Ping :)