* Add testing helpers for comparing diagnostics with different levels of stringency
* Refactor some existing tests to use the new helpers
* Replace use of diag comparison test helpers in terraform package
* Add header
* Add return statement back in ephemeral test
* Update internal/terraform/context_plan2_test.go
* Add `DiagnosticComparer` to standardize how diagnostics are compared for equality. This uses code originally in the s3 backend.
Co-authored-by: Graham Davison <gdavison@hashicorp.com>
* Refactor `test` related code to use new comparer
* Refactor `s3` related code to use new comparer
* Replace use of reflect and go-spew with new diagnostics comparison approach
* Fix whitespace
* Make `tfdiags.DiagnosticComparer` a var
* Fix DiagnosticComparer test
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Co-authored-by: Graham Davison <gdavison@hashicorp.com>
