Allow running Check tests on imported resources

[greentruff]

SDK version

v1.15.0

I checked 2.4.4 and the behavior for imported tests is identical, state is not modified.

Use-cases

The terraform plugin for datadog supports modifying certain properties of default rules. Default rules cannot be created by users and are instead a special resource which must be imported before being modified. See documentation the documentation here.

Implementation of the resource is here

We would like to implement tests which check that the fields are being modified correctly.

Attempted Solutions

The existing tests misused the test framework and use both ImportState: True and Check. The Checks are ignored in this case, testing with ImportStateCheck the state is right after import and does not take into account other changes on top of it. It is also not possible to split the check into multiple steps as ImportState will revert back to the previous state after an import step.

Proposal

Add a flag to keep state after an import step such as ImportPersistState: True which returns the updated state so that following steps can modify it.

References

[bflad]

Thanks so much for filing this, @greentruff and this is a great idea! Apologies for the long delay in responding.

I believe our preference here would be something as you mention in your proposal, a new ImportState* flag that can be added during the "import TestStep mode". Then provider developers would be able to do something like:

resource.TestCase{
  // ... other fields omitted for brevity ...
  Steps: []resource.TestStep{
    // Importing TestStep
    {
      ImportState:       true,
      ImportStateId:     /* required if first TestStep */,
      ImportStateVerify: true,
      Config: /* required if first TestStep */,
      ImportStatePersist: true, // <-- New flag to trigger "keeping" the imported state
    },
    // Checking TestStep
    {
      Config: /* ... */,
      Check: /* ... */,
    },
  },
}

Naming suggestions are welcome, but I think aligning with the other ImportState* ones will suffice for now. A future iteration of the testing framework can clean up the TestStep implementations so its clearer which are meant for "apply" steps versus "import" steps.

One detail we do need to capture in provider defined implementations is that if there is no prior state, then the Config and ImportStateId* are required, which should be enforced by the testing framework.

Thanks again!

[sebasslash]

Hi @bflad! Can confirm a solution like this would also be beneficial for our use case in terraform-provider-tfe, where we need to create resources externally, import them and then subsequently test against these resources. Ideally, I'd like to be able to reuse state from the import step(s) in later test steps -- so I think ImportStatePersist: true would work really well here. ❤️

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