Write unit tests for soy.textures.Texture, specifically testing atomic changes, resizing, and channel changing.

At least two of these tests should currently fail since the code for resizing and channel changing is incomplete, though the completion of "Scale Texture on Resize" should fix that. There is no inter-dependency between these two tasks as the API for changing the size and channels will not be changed by either.

While working on this task you should join and remain in #PySoy on Freenode to get help, feedback, and guidance from mentors and other developers. Code updates which may affect your work are also announced here as they happen.

When you've done, commit your work and post the resulting changeset url to this task.