Migrate from JUnit to Spock for unit tests

[ultraq]

I was introduced to Spock at SpringOne 2GX and really liked what I saw :) Let's see if I can migrate my JUnit tests to Spock ones for this project, given that most of the JUnit test code is boilerplate to redirect to the Thymeleaf testing library.

[ultraq]

Might wanna hold out on this one until I see what becomes of this issue: thymeleaf/thymeleaf-testing#7

[ultraq]

Also might want to wait to see if I do a Groovy rewrite of this plugin - Spock is pretty good when using it's Groovy DSL.

[ultraq]

Gave the rewrite a try, and it didn't really do much except add a 3MB dependency (groovy) to the project! Probably not worth the added weight just to make me feel a bit better about the null/empty checks.