I am programming PHP since nearly 20 years, Yii since 3 years - not professional, but as a timeconsuming hobby 
I never tested - I only debugged my code. Since some weeks I try to learn testing with PHPUnit and it’s hard for a beginner to get a good overview. Struggling hard I don’t want to give up - but it’s frustrating, the learncurve low. 
Are here other people around who are testing their Yii-code? What are your experiences? Which limitations did you find?
My tools till now: PHPUnit + Mockery
Which tools do you use?
Hope that I’m not alone here and get some encouraging words