Full coverage for CSharpSnapshotGenerator

[ajcvickers]

Since we have had a few bugs in this area.

[bricelam]

I think our biggest problem is forgetting to add coverage when we add new features. It would be nice if we had one set of tests for both model building and round-tripping through the snapshot.

[bricelam]

For example:

Test(
    mb => mb.Entity<MyEntity>.Property(e => e.MyProperty).HasCollation("MY_COLLATION"),
    model =>
    {
        Assert.Equal("MY_COLLATION", model.GetEntityType("MyEntity").GetProperty("MyProperty").Collation);
    });

The assert could be run both against regular model building, and through the model that comes back from the compiled snapshot.

[AndriySvyryd]

I think our biggest problem is forgetting to add coverage when we add new features. It would be nice if we had one set of tests for both model building and round-tripping through the snapshot.

I am reluctant to add too many snapshot tests as on average they are 17 times slower than pure model building tests

[AndriySvyryd]

Converting all model building tests would increase testing time by almost 20 minutes