[meta] 2.x test coverage

Test coverage at 2.x is fairly good but there are places where it can be expanded. This meta issue is the parent for all 2.x test coverage work.

The child issues may also be appropriate for 8.x-1.x and if so, they should specify #2712465: [meta] 8.x-1.x test coverage as a 'related' issue, because an issue can only have one 'parent'