test: Add missing unit tests in vtctl/workflow

[beingnoble03]

Description

This PR adds missing unit tests for resharder.go

The code coverage in main:

coverage: 59.8% of statements in vitess.io/vitess/go/vt/vtctl/workflow...
ok  	vitess.io/vitess/go/vt/vtctl/workflow	2.869s	coverage: 59.8% of statements in vitess.io/vitess/go/vt/vtctl/workflow...

The code coverage in this branch:

coverage: 60.6% of statements in vitess.io/vitess/go/vt/vtctl/workflow...
ok  	vitess.io/vitess/go/vt/vtctl/workflow	2.805s	coverage: 60.6% of statements in vitess.io/vitess/go/vt/vtctl/workflow...

Cmd used:

go test ./go/vt/vttablet/tabletmanager ./go/vt/vtctl/workflow -v -coverpkg=vitess.io/vitess/go/vt/vtctl/workflow... -coverprofile=c.out

Related Issue(s)

• Tracking Issue: vtctldclient/vtctld: Enhance test coverage and code refactor  #16499

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

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• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
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If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[mattlord]

We should clean it up:

defer env.close()

[beingnoble03]

done.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.44%. Comparing base (0726ea6) to head (dce0c38).
Report is 20 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17304      +/-   ##
==========================================
+ Coverage   67.40%   67.44%   +0.03%     
==========================================
  Files        1574     1576       +2     
  Lines      253221   253417     +196     
==========================================
+ Hits       170690   170914     +224     
+ Misses      82531    82503      -28     

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