Enable envtest-based unit tests for webhooks

[sbueringer]

User Story

As a developer I would like to be able to write unit tests with envtest for our webhooks.

Note: In case of webhooks the fakeclient unit tests have (at least) the following limitations:

• The webhooks cannot use indices (as that's not supported by fakeclient)
• There is no marshalling/unmarshalling of Go types and no OpenAPI schema validation of the kube-apiserver as we directly call validate/default funcs with our structs. Especially with ClusterClass variables this can lead to cases where the unit test is successful but the apiserver would reject the create/update call without even asking the webhook

Detailed Description

I would suggest implementing it the same way we currently add indices to our testenv:

• create helper functions to register webhooks
• Add a SetupWebhooks func to RunInput (used in internal/envtest.Run)

This solution would enable envtest-based unit test for all our webhook packages except top-level api/v1beta1, because this would lead to a circular dependency between api/v1beta and webhooks. But we already have this limitation today and if we want to unit test one of the webhooks in the api/v1beta1 package with envtest we can simply move it to the webhooks package.

/kind feature

[sbueringer]

Note: #5719 depends on this issue

[sbueringer]

@fabriziopandini WDYT?

[sbueringer]

Just realized that the idea might sound good in theory, but that we have way too many api packages. So we still would have to call 6 setup funcs whenever we use SetupWebhooks. I'll come up with an alternative approach

[sbueringer]

PR #5722 represents a potential solution by refactoring the envtest package.

I've discussed the issue with Fabrizio and we would simply implement the webhooks integration test in a package like internal/webhooks/integration instead of refactoring envtest like proposed in the PR.

The problem with the changes proposed in the PR is that they would distribute the webhook setup all over the place vs. currently webhooks will just work out of the box when using envtest.

[sbueringer]

We're now implementing the first integration tests in internal/webhooks/test.

I'm not sure if we should keep this issue around for further discussions or close it for now.

@fabriziopandini @killianmuldoon WDYT?

[killianmuldoon]

I think we close this discussion for now - if it comes up again we can open a new issue, but for the webhook case we have something that works for now.

[sbueringer]

/close

[k8s-ci-robot]

@sbueringer: Closing this issue.

In response to this:

/close

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