Added partial unit tests

Here are the tests written on testfest
Though it won't break anything I notice that you have the arguments in the wrong order for the assertEquals. When unit testing the expected value (in you case 'Foo bar') is supposed to be the first argument and the actual result (which you call $expectContent) is the second.

In this case it will not influence the test but you may get confused when reading the PHPUnit output, or when using other asserts it may give errors.