add unit tests (and slight tweak) for ocean wave utils

[mbkuhn]

Summary

I wasn't sure if I could trust some of these functions, so I wrote unit tests. Turns out they're good.

I made a slight tweak but it shouldn't make a difference because of conditionals elsewhere when the function is called.

Pull request type

Please check the type of change introduced:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe): better unit test coverage

Checklist

The following is included:

• new unit-test(s)
• new regression test(s)
• documentation for new capability

This PR was tested by running:

• the unit tests
  • on GPU
  • on CPU
• the regression tests
  • on GPU
  • on CPU