add unit test for function (#746)

[csynineyang]

What this PR does:

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Patch coverage: 83.33% and project coverage change: +0.93% 🎉

Comparison is base (304e9ff) 38.38% compared to head (4a0d088) 39.32%.
Report is 2 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #756      +/-   ##
==========================================
+ Coverage   38.38%   39.32%   +0.93%     
==========================================
  Files         254      259       +5     
  Lines       26359    26502     +143     
==========================================
+ Hits        10119    10422     +303     
+ Misses      15121    14946     -175     
- Partials     1119     1134      +15     

Files Changed	Coverage Δ
pkg/runtime/namespace/namespace.go	67.59% <83.33%> (+20.33%)	⬆️

... and 10 files with indirect coverage changes

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[sonarcloud]

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0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication