mail/components/extensionsis tested by tests in
mail/components/extensions/test. Inside the
testdirectory is a subdirectory named after the type of test:
browserfor mochitests (as in Firefox terms they are "browser-chrome" mochitests), and
unitfor XPCShell tests.
head.jsfile if you're going to have more than one test.
moz.buildfile, add these lines as appropriate: