etcdctl: add fake client for UT

[hwdef]

Part of: #20171

/cc @siyuanfoundation @Elbehery

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @hwdef. Thanks for your PR.

I'm waiting for a etcd-io member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[siyuanfoundation]

/ok-to-test

[codecov[bot]]

Codecov Report

:x: Patch coverage is 64.04494% with 32 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 69.61%. Comparing base (584c7cc) to head (983a7ad).

Files with missing lines	Patch %	Lines
etcdctl/ctlv3/command/fakeclient/client.go	32.25%	21 Missing :warning:
etcdctl/ctlv3/command/global.go	81.81%	5 Missing and 3 partials :warning:
etcdctl/ctlv3/command/test_utils.go	84.61%	1 Missing and 1 partial :warning:
etcdctl/ctlv3/ctl.go	0.00%	1 Missing :warning:

Additional details and impacted files

Files with missing lines	Coverage Δ
etcdctl/ctlv3/ctl.go	0.00% <0.00%> (ø)
etcdctl/ctlv3/command/test_utils.go	84.61% <84.61%> (ø)
etcdctl/ctlv3/command/global.go	52.17% <81.81%> (+52.17%)	:arrow_up:
etcdctl/ctlv3/command/fakeclient/client.go	32.25% <32.25%> (ø)

... and 27 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #20270      +/-   ##
==========================================
+ Coverage   69.16%   69.61%   +0.44%     
==========================================
  Files         422      424       +2     
  Lines       34841    34907      +66     
==========================================
+ Hits        24098    24300     +202     
+ Misses       9339     9162     -177     
- Partials     1404     1445      +41     

---

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[hwdef]

@siyuanfoundation @Elbehery @serathius PTAL. This PR is ready for review :)

[siyuanfoundation]

Overall this approach works. But if the tests run in parallel, there will be race condition on the var newClientFunc. To ensure only 1 test runs at a time, we will need to add a new test suite in test.sh with go test -p 1.

Another option would be refactor all the functions like NewAlarmCommand to take a client argument. Personally I would prefer this.

@ahrtr would really appreciate your input. Thanks!

[hwdef]

/retest

[hwdef]

PTAL @ahrtr @Elbehery