I was confused about the differences among:
srcDir 'foo'
srcDirs ['foo']
srcDirs = ['foo']
As it turns out, the first two append to the set of source
directories, while the last replaces this set entirely. I generally
want replacement, since WALA's current directory layout never matches
Gradle's assumed defaults.
The main requirement here is to arrange for the proper classpath
settings when tests are running so that they can find any associated
resources (i.e., other supporting files).