test: add tests for negative values in math/base/special/fmod

[gunjjoshi]

Description

What is the purpose of this pull request?

This pull request:

• adds tests for negative values in math/base/special/fmod.
• includes indentation fixes
• addresses other suggestions from 8558d86#commitcomment-144215763

Related Issues

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None.

Questions

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No.

Other

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• I have changed the function that we used to generate test fixtures in julia, from mod to rem. This is because, rem handles negative values in a much better way.
• When I made this change, the behavior of the function in main.c changed, yielding failures in tests. So, I kept it the same.

Checklist

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• Read, understood, and followed the contributing guidelines.

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@stdlib-js/reviewers

[kgryte]

rem seems to be the correct function to test against (ref: JuliaLang/julia#47501), as rem is the native Julia equivalent of fmod. The alternative is not to test against Julia and actually just test against the C standard library directly, as fmod was added in C99. Looking at https://github.com/stdlib-js/stdlib/tree/164a96b61fa0cdd442c29d2af3979033acada25e/tools/snippets/test/fixtures, however, and it seems we don't have a fixture generation script for testing against the C standard library.

[kgryte]

LGTM. Thanks, @gunjjoshi!