add some ut 4 gopkgs

[TremblingV5]

Link to an issue

What

How

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How to test

Checklist

• [ ] Link to an issue if it really related.
• [ ] At least describe what this PR does.
• [ ] Use rebase to confirm that current branch doesn't conflict with main branch.
• [ ] Unit tests. At least do not reduce the unit test coverage.
• [ ] Checked and updated guidelines.md which used to describe how to build, deploy and use DouTok.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 25.00000% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
backend/gopkgs/cachex/cache.go	0.00%	9 Missing :warning:

Files with missing lines	Coverage Δ
backend/gopkgs/gofer/gofer.go	43.58% <100.00%> (ø)
backend/gopkgs/cachex/cache.go	0.00% <0.00%> (ø)