Add a test.File function for comparing expected file contents

[FollowTheProcess]

Description

Motivation and Context

Closes #

How Has This Been Tested?

Checklist

• [ ] I have updated the documentation if needed.
• [ ] I have updated the tests if needed.

[codecov[bot]]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (0986fff) 96.20% compared to head (8fdc6db) 93.25%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #12 +/- ## ========================================== - Coverage 96.20% 93.25% -2.95% ========================================== Files 1 1 Lines 79 89 +10 ========================================== + Hits 76 83 +7 - Misses 2 4 +2 - Partials 1 2 +1 ``` | [Files](https://app.codecov.io/gh/FollowTheProcess/test/pull/12?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tom+Fleet) | Coverage Δ | | |---|---|---| | [test.go](https://app.codecov.io/gh/FollowTheProcess/test/pull/12?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tom+Fleet#diff-dGVzdC5nbw==) | `93.25% <70.00%> (-2.95%)` | :arrow_down: |

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