pass: improve error-handling in tests, and don't fail early

[thaJeztah]

• extracting this from https://github.com/docker/docker-credential-helpers/pull/275, because it looks like we're missing pass on macOS and Windows, and as a results, tests were not actually doing anything

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -12.03 :warning:

Comparison is base (4ede49c) 55.55% compared to head (bc53080) 43.52%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #277 +/- ## =========================================== - Coverage 55.55% 43.52% -12.03% =========================================== Files 9 7 -2 Lines 666 448 -218 =========================================== - Hits 370 195 -175 + Misses 253 222 -31 + Partials 43 31 -12 ``` [see 3 files with indirect coverage changes](https://app.codecov.io/gh/docker/docker-credential-helpers/pull/277/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=docker)

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[thaJeztah]

For macOS there's a brew formula; https://www.passwordstore.org/#macintosh that we could possibly use

[thaJeztah]

superseded by https://github.com/docker/docker-credential-helpers/pull/289