Describe how to test a beta-only field of the resource generated by mmv1

[shotarok]

Background

This is a feature request to add a description of how to test a beta-only field of the resource generated by mmv1. It took time for me to understand how to test a beta-only field. Updating a doc would help developers to define a new beta field in the future.

What kind of contribution is this issue about?

• MMv1-based resource

Related PR(s), if any:

• Promote Vertex AI FeatureStore resources (GA only) GoogleCloudPlatform/magic-modules#6565

Details

In the above PR#6565, I needed to add a test for a beta-only field. I spent time reading the mmv1 code, and I understood adding min_version: beta to !ruby/object:Provider::Terraform::Examples generates a test in the beta provider, but not in the ga provider.

Therefore, I ended up defining two examples to test the beta-only field. One is without the beta-only field, which works for the ga and beta providers. Another is with the beta-only field, which works for the beta provider.

I'm not sure if this strategy is the best approach, but that'd be great if a doc in the magic-module repo has the description of how to test the beta-only field.

[shotarok]

It'd be good to add how to test the beta-only field to the following section: https://github.com/GoogleCloudPlatform/magic-modules/tree/main/mmv1#adding-beta-fields or https://github.com/GoogleCloudPlatform/magic-modules/tree/main/mmv1#tests-that-use-a-beta-feature.