supply some unit tests to increase the code coverage

[haoel]

The unit tests for

• pkg/util/ratelimiter
• pkg/util/circuitbreaker
• pkg/util/agent_controller
• pkg/util/texttemplate
• pkg/common/utils
• pkg/common/strings
• pkg/common/options
• pkg/common/time
• pkg/common/stat_aggregator
• pkg/common/go
• pkg/common/callback

[codecov-commenter]

Codecov Report

Merging #133 (7b1970d) into main (f941a2c) will increase coverage by 13.07%.
The diff coverage is 59.37%.

@@             Coverage Diff             @@
##             main     #133       +/-   ##
===========================================
+ Coverage   46.55%   59.63%   +13.07%     
===========================================
  Files          38       38               
  Lines        2586     2601       +15     
===========================================
+ Hits         1204     1551      +347     
+ Misses       1302      940      -362     
- Partials       80      110       +30     

Impacted Files	Coverage Δ
pkg/common/stat_aggregator.go	65.48% <0.00%> (+3.53%)	⬆️
pkg/util/jmxtool/agent_controller.go	48.88% <35.71%> (+48.88%)	⬆️
pkg/util/circuitbreaker/circuitbreaker.go	79.50% <90.90%> (+16.61%)	⬆️
pkg/util/ratelimiter/ratelimiter.go	89.65% <100.00%> (+30.00%)	⬆️
pkg/util/texttemplate/texttemplate.go	75.83% <0.00%> (+4.69%)	⬆️
pkg/util/jmxtool/common.go	69.81% <0.00%> (+20.75%)	⬆️
pkg/util/urlrule/urlrule.go	82.50% <0.00%> (+35.00%)	⬆️
... and 9 more

---

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[benja-wu]

LGTM