Add group snapshot controller unit tests

[leonardoce]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change /kind bug /kind cleanup /kind design /kind documentation /kind failing-test /kind feature /kind flake

What this PR does / why we need it:

Adds unit tests for the group snapshot controller.

Which issue(s) this PR fixes:

Fixes #1082

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Skipping CI for Draft Pull Request. If you want CI signal for your change, please convert it to an actual PR. You can still manually trigger a test run with /test all

[leonardoce]

I would suggest to add the test for create,delete, update in single file

Thank you, @yati1998, for having a look. I split the unit tests because that's what it was done for volume snapshots. Do you think it would better for volume group snapshots to have a different approach?

[leonardoce]

Thank you @Madhu-1!

[leonardoce]

Done @xing-yang, and thanks for the advice. I also added another test for pre-provisioned volume group snapshots, testing the mismatch between a pre-provisioned volume group snapshot and a dynamically-provisioned volume group snapshot content.

[xing-yang]

/lgtm /approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: leonardoce, xing-yang

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