Create tests for the most common use cases

[alshakero]

Hi,

This PR proposes a few tests for the snapshot.js file. This will hopefully make the development process a little safer and more rigorous.

Once this PR is approved, or more tests are suggested, we could then send minor patches such as #16 without less risk on affecting the service stability.

Soon, after this, I'll add a failing test for #16, then I'll send a patch to make it pass.

Thanks!

[deBhal]

Looks good to me! I'm going to go ahead and merge with two notes:

I spoke with @darthhexx yesterday, and he stressed the importance of tests covering the php<->js and back because the php does additional processing on the image, so it'd be great if we could add those.

Having said that, it's not an either/or scenario, and these tests still seem valuable on their own merit, so I'm going to go ahead and merge this PR into master (we can always revert later if we need to).

The other thing is that I'm still a bit scarred from maintaining tests with sleep()s, so I've pushed #20 that favors listening to messages from the queue. This doesn't make a huge difference immediately, so I've made a new PR instead of updating this one. I'd love a review!