[Feature] Implement adapter tests in dbt-postgres

[colin-rogers-dbt]

Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward extension of existing dbt-postgres functionality, rather than a Big Idea better suited to a discussion

Describe the feature

Currently dbt-postgres has implemented dbt-core's tests but doesn't reference the dbt-tests-adapter tests.

Describe alternatives you've considered

No response

Who will this benefit?

No response

Are you interested in contributing this feature?

No response

Anything else?

No response

Tasks

Preview Give feedback

1. Create separate base classes for shared tests dbt-adapters#93
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2. Setup shared tests #18
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[mikealfare]

Re-opening to resolve issues that were discovered in the original migration.