refactor: introduce golden file testing to simplify test expectation updates

[rindrics]

Summary

This PR introduces golden file testing across test packages (api/resource, api/resmap, and api/krusty) to simplify updating test expectations when YAML output order changes. This change prepares for PR #6046, which will modify Resource.AsYAML() behavior and is expected to change the output order of generated YAML resources.

Background

PR #6046 changes Resource.AsYAML() to use RNode.MustString() instead of sigs.k8s.io/yaml.JSONToYAML. This change will preserve the original YAML field order instead of sorting fields alphabetically, which will affect the output order of generated resources.

While both orderings are valid YAML, this change requires updating many test expectations to match the new output order. To make these updates easier and more maintainable, we are introducing golden file testing, which separates test expectations from test code and allows for easy updates using a simple flag.

Benefits

1. Easier test expectation updates: When PR fix: preserve original YAML formatting in resource output #6046 changes YAML output order, test expectations can be updated by simply running tests with -update-golden flag instead of manually editing test code
2. Better test maintainability: Golden files separate test expectations from test logic, making it easier to review changes and understand what the tests are verifying
3. Improved readability: Test code becomes more concise without large inline YAML strings
4. Future-proof: Golden files make it easier to handle future changes to output formatting or ordering

Testing

All tests pass with the new golden file infrastructure:

# Run all tests
cd api && go test -v -timeout 45m -cover ./... -ldflags "-X sigs.k8s.io/kustomize/api/provenance.buildDate=2023-01-31T23:38:41Z -X sigs.k8s.io/kustomize/api/provenance.version=(test)"

# Update golden files (when needed after PR #6046)
go test ./api/resource -update-golden -ldflags "..."
go test ./api/resmap -update-golden -ldflags "..."
go test ./api/krusty -update-golden -ldflags "..."

Related PRs and Issues

• Prepares for PR fix: preserve original YAML formatting in resource output #6046: Changes Resource.AsYAML() to use RNode.MustString() to preserve original YAML formatting
• Related to Line breaks on long strings with spaces #947: Long lines with spaces wrapping issue (will be fixed in PR fix: preserve original YAML formatting in resource output #6046)

Migration Notes

This PR does not change any test behavior or expected outputs. It only changes how test expectations are stored and compared. After PR #6046 is merged, golden files can be updated using the -update-golden flag to reflect the new YAML output order.

[k8s-ci-robot]

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[k8s-ci-robot]

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[k8s-ci-robot]

Hi @rindrics. Thanks for your PR.

I'm waiting for a kubernetes-sigs 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.

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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.

[rindrics]

@koba1t @sarab97 @varshaprasad96 would you accept this PR to run CI tests?

[koba1t]

/ok-to-test

[rindrics]

@koba1t @sarab97 @varshaprasad96
Is there anything I can do to help complete the status check and move this pull request forward?
thanks.