Add more tests

[ThomasWall03]

How to categorize this PR?

/kind enhancement

What this PR does / why we need it:
This PR adds Unit tests to several files.

Furthermore, the generated files for mocking are excluded from make test-cov.

Increased the test coverage from 15.8% to 17.6%

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
Gomock is used for the first time in this repository for the tests of utils_certificate. It mocks resources.Object and the generated mock file is provided in pkg/cert/utils/mock.

Release note:

NONE

[gardener-prow]

Hi @ThomasWall03. Thanks for your PR.

I'm waiting for a gardener 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.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[gardener-robot-ci-3]

Thank you @ThomasWall03 for your contribution. Before I can start building your PR, a member of the organization must set the required label(s) {'reviewed/ok-to-test'}. Once started, you can check the build status in the PR checks section below.

[marc1404]

/ok-to-test

[marc1404]

Thanks for addressing the suggestions!

/lgtm

[gardener-prow]

LGTM label has been added.

Git tree hash: ee7f835f3fb46b010c5fa9175a83dec0b152322a

[marc1404]

@ThomasWall03 make check is failing in CI:

Running go vet...
running code generator...
go build -o hack/tools/bin/linux-amd64/vgopath github.com/ironcore-dev/vgopath
go: downloading github.com/ironcore-dev/vgopath v0.1.5
go build -o hack/tools/bin/linux-amd64/controller-gen sigs.k8s.io/controller-tools/cmd/controller-gen
go: downloading sigs.k8s.io/controller-tools v0.16.5
go: downloading github.com/gobuffalo/flect v1.0.3
go: downloading k8s.io/gengo/v2 v2.0.0-20240228010128-51d4e06bde70
go: downloading golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d
go: downloading golang.org/x/sync v0.7.0
go: downloading golang.org/x/mod v0.17.0
Generating deepcopy code for 1 targets
go: downloading golang.org/x/text v0.16.0
go: downloading github.com/google/gnostic-models v0.6.8
go: downloading k8s.io/kube-openapi v0.0.0-20240228011516-70dd3763d340
go: downloading github.com/go-openapi/jsonreference v0.20.2
go: downloading sigs.k8s.io/structured-merge-diff/v4 v4.4.1
go: downloading github.com/go-openapi/swag v0.22.4
go: downloading github.com/go-openapi/jsonpointer v0.19.6
Generating client code for 1 targets
grep: ./hack/../pkg/client/cert/clientset: No such file or directory
Generating lister code for 1 targets
grep: ./hack/../pkg/client/cert/listers: No such file or directory
Generating informer code for 1 targets
grep: ./hack/../pkg/client/cert/informers: No such file or directory
pkg/cert/utils/mock/doc.go:5: running "mockgen": exec: "mockgen": executable file not found in $PATH
make: *** [Makefile:85: generate] Error 1

[gardener-prow]

New changes are detected. LGTM label has been removed.

[gardener-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
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[marc1404]

/ok-to-test

[marc1404]

/ok-to-test