When defining properties I also verify how the property is actually used to make the best decision. In this specific case it appears that the property is never read from, which indicates that the better fix might be removing the assignment. However because of the failing test suite I was not able to properly verify this.

@TimWolla I agree with what you're saying. However, as you've alluded to, without tests and anyone with knowledge of simpletest internals such changes are just asking for trouble. I think it's better to just maintain how things worked before. A dynamic property was previously declared public, so public $foo is the way to go.

Based on other classes private $expected_args; would probably also work, but again, it's difficult to know whether that dynamic property is used elsewhere.