Migrations: Test using snapshot

[AndriySvyryd]

The test suite with most scenarios for migrations - MigrationsModelDifferTest currently doesn't use the product pipeline to run the tests. It creates two models and then diffs them. Whereas the product generates a snapshot of the first model, compiles it, loads it and then diffs it with the second model.

The model snapshot could be significantly different from the model (e.g. it uses different CLR types for properties that have a value conversion). And we are missing cases where the generated code doesn't compile at all.

However doing this for every test case might be too slow.

[roji]

Is this a dup of #20157?

[smitpatel]

@roji - They are related.
Source model should be built from a snapshot. (tracked here)
Target model should be built using conventions (tracked in #20157)

[roji]

OK, probably good to tackle together...

[ajcvickers]

See also:

• Build target model with conventions in MigrationsTestBase Build models with conventions in MigrationsTestBase #20157
• Remaining clean up for migration tests Remaining clean up for migration tests #19668

[roji]

Poaching