Use a real struct (not named struct) in ExMachinaTest
Use a real struct (not named struct) in ExMachinaTest

We used to have a struct factory defined as `%{__struct__: FooBar}` but
it was confusing since the factory name was `struct_factory`.

So we change to be `foo_bar_factory` and create a module with a struct
called `FooBar`. This has the benefit of allowing us to assert
`%FooBar{}` in tests -- something we couldn't do with the previous
format.

thoughtbot/ex_machina