Migrations: Improve functional test coverage

[rowanmiller]

Probably by porting existing tests from EF6

[bricelam]

Here are some scenarios I want to cover.

• CSharpMigrationOperationGenerator can round-trip operations through the compiler
• ModelDiffer can detect operations
  • ...and handle entity or property renames
  • ...and table or column renames
  • ...and sort correctly
• MigrationSqlGenerator can apply operations to the database
• Migrator can apply and revert migrations

[roji]

Just wanted to know the state of migration functional tests before attacking migrations in PostgreSQL... There seem to be some non-inherited migration tests within each provider's testsuite but nothing comprehensive I can actually use. Should I wait a bit, are there plans to work on this?

[bricelam]

@roji, So far, there are just unit tests to verify the SQL. You can copy these to use in your own unit tests. I also plan to create some provider-inheritable functional tests. I started in bricelam:migtests, but they were way too slow! We have some ideas on how to do it faster, but I haven't gotten around to implementing it yet.

[bricelam]

I've added some basic functional tests that cover the HistoryRepository in #2733

[bricelam]

Closing. I feel like our coverage is pretty decent now. We'll rely on app building, exploratory testing, and code coverage analysis for more. Creating more provider-agnostic tests will be done as part of #1807.