🌱 Implement unit-tests for desired state generator

[Karthik-K-N]

What this PR does / why we need it:

Adds UT for desired state generator function

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #12614

/area testing

[k8s-ci-robot]

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[Karthik-K-N]

@sbueringer Added a basic case, Could you please help me withe the use cases you wish to cover here. Thanks

[k8s-ci-robot]

@Karthik-K-N: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-e2e-blocking-main	a429eb6	link	true	/test pull-cluster-api-e2e-blocking-main

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[chrischdi]

/retitle 🌱 Implement unit-tests for desired state generator