helper/resource: Add ParallelTest() function to allow opt-in acceptance testing concurrency with t.Parallel()

[bflad]

Please note: this is an alternate implementation to #16807, using a separate function rather than requiring adjustment to each existing TestCase and submitted just for an additional reference point. The preferred solution may be either implementation or a combination of the two! I think more importantly we should continue the conversation for supporting this type of functionality as its been implemented or requested by a few of the major providers. 😄

While this initial implementation is a very simple wrapper function, implementing this in the helper/resource package provides some downstream benefits:

• Provides a standard interface for plugin developers to enable parallel acceptance testing
• Existing plugins can simply convert resource.Test to resource.ParallelTest references (as appropriate) to enable the functionality, rather than worrying about additional line(s) to each acceptance test function or TestCase
• Potential enhancements to ParallelTest (e.g. adding an environment variable to skip enabling the behavior) are consistently propagated

[paddycarver]

I can't believe I didn't think of that before adding t.Parallel() to hundreds of tests. 😓

[MalloZup]

@bflad what is the next step for this PR to get merged? i really like this feature and could help us in our terraform libvirt provider having this to the schema helper

Thank you for your attention. Have nice day.! 🌞 🌻

[appilon]

This seems reasonable to me, providers can opt-in 1 test at a time. I'm not an authority on core though so I would prefer see another approval maybe? But I will get it started.

[apparentlymart]

This doesn't have any implications for Terraform Core, but indeed LGTM!

[MalloZup]

Thanks :love:

[tombuildsstuff]

LGTM 👍

[bflad]

Thanks, everyone!! 🚀

[MalloZup]

🚀 🎸 🎉

[metacpp]

@bflad thanks for the fantastic work!

One more thing to take care: the output of testing result is a known issue for go test running in parallel. Please visit golang/go#19280 for the details. The proposal is to output test result in a structural (for example, JSON) format, see golang/go#2981. And it was released in v1.10 through go test -json, we need to remind provider developer for this.

[ghost]

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