What is the checkup app?
It’s an app developed by Fairphone to test many of the functions of the phone to determine whether you have a hardware or software issue.
Where can I find it on my FP2?
On standard Fairphone OS and Fairphone Open OS it is preinstalled and integrated in the Settings app. You can find it under Settings -> Maintenance -> Checkup.
On other OSes and even on non-Fairphones you can download the app e.g. from F-Droid.
What about the FP1?
On the FP1 there is the #dic:testingmode with lots of the similar tests.
The checkup app can’t be installed on an FP1, since it needs Android 5.1 or higher.