Add exported function to retrieve attribute from state for use during tests

[bendbennett]

SDK version

v2.20.0

Use-cases

Occasionally, when writing acceptance tests it is useful to be able to extract and store a value from state in order to use in subsequent test steps. For instance, when using the Taint field in a TestStep it is useful to be able to verify that a resource has been destroyed and recreated.

Attempted Solutions

Adding a function along the following lines to each provider which needs to be able to compare attributes before and after test steps.

func testExtractResourceAttr(resourceName string, attributeName string, attributeValue *string) r.TestCheckFunc {
	return func(s *terraform.State) error {
		rs, ok := s.RootModule().Resources[resourceName]

		if !ok {
			return fmt.Errorf("resource name %s not found in state", resourceName)
		}

		attrValue, ok := rs.Primary.Attributes[attributeName]

		if !ok {
			return fmt.Errorf("attribute %s not found in resource %s state", attributeName, resourceName)
		}

		*attributeValue = attrValue

		return nil
	}
}

Proposal

Add an exported function to /helper/resource that exposes this functionality to avoid code duplication in providers.

References

[bflad]

We've certainly seen providers that use this class of attribute value extraction across TestStep. 😄 I'm wondering if its worth investigating this enhancement against the context of these as well:

• https://github.com/hashicorp/terraform-plugin-sdk/issues/77
• https://github.com/hashicorp/terraform-plugin-sdk/issues/236
• https://github.com/hashicorp/terraform-plugin-sdk/issues/482

They're all circling around verifying the resource under test was planned for and/or deleted/recreated properly. More easily enabling provider developers to extract values and perform their own equivalence testing certainly is interesting.