tests: add tests for SHA256

[vil02]

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Describe your change:

This PR adds tests for SHA256.
The data was verified with https://emn178.github.io/online-tools/sha256.html.

Similar to #1602.

• Add missing tests.

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new JavaScript files are placed inside an existing directory.
• All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames.
  Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6aaa376) 82.44% compared to head (dbabed8) 83.44%.

Additional details and impacted files

@@ Coverage Diff @@## master #1604 +/- ## ========================================== + Coverage 82.44% 83.44% +0.99%  ========================================== Files 377 377 Lines 19747 19747 Branches 2884 2906 +22 ========================================== + Hits 16281 16477 +196 + Misses 3466 3270 -196 

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[appgurueu]

Verified using the sha256sum command.