Add unit tests for com.alibaba.csp.sentinel.util

[paulkennethkent]

This test was written using Diffblue Cover.

Describe what this PR does / why we need it

I've analysed your code base and noticed that com.alibaba.csp.sentinel.util.IdUtil and com.alibaba.csp.sentinel.util.StringUtil are not fully tested.

Describe how you did it

I've written some tests for the functions in this class with the help of Diffblue Cover. Hopefully, these tests should help you detect any regressions caused by future code changes. If you would find it useful to have additional tests written for this repository, I would be more than happy to look at other particular classes that you consider important.

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #651 into master will increase coverage by 0.21%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #651      +/-   ##
============================================
+ Coverage     40.41%   40.62%   +0.21%     
- Complexity     1187     1320     +133     
============================================
  Files           267      284      +17     
  Lines          7852     8923    +1071     
  Branches       1062     1193     +131     
============================================
+ Hits           3173     3625     +452     
- Misses         4281     4843     +562     
- Partials        398      455      +57

Impacted Files	Coverage Δ	Complexity Δ
.../alibaba/csp/sentinel/eagleeye/FastDateFormat.java	78.37% <0%> (ø)	6% <0%> (?)
...com/alibaba/csp/sentinel/eagleeye/TokenBucket.java	35.29% <0%> (ø)	1% <0%> (?)
...a/csp/sentinel/slots/statistic/base/Striped64.java	26.04% <0%> (ø)	5% <0%> (?)
...libaba/csp/sentinel/eagleeye/EagleEyeAppender.java	14.28% <0%> (ø)	1% <0%> (?)
...sentinel/eagleeye/EagleEyeRollingFileAppender.java	28.9% <0%> (ø)	11% <0%> (?)
...a/com/alibaba/csp/sentinel/eagleeye/StatEntry.java	20.21% <0%> (ø)	8% <0%> (?)
...om/alibaba/csp/sentinel/eagleeye/SyncAppender.java	53.57% <0%> (ø)	5% <0%> (?)
...ibaba/csp/sentinel/eagleeye/StatLogController.java	65.93% <0%> (ø)	5% <0%> (?)
...va/com/alibaba/csp/sentinel/eagleeye/EagleEye.java	39.47% <0%> (ø)	11% <0%> (?)
.../com/alibaba/csp/sentinel/eagleeye/StatLogger.java	66.66% <0%> (ø)	11% <0%> (?)
... and 11 more

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[sczyh30]

LGTM

[sczyh30]

Thanks!