Seventh Imam, Imam Musa al Kadhim ( a.s) says:

مَثَلُ الْمُؤْمِنِ مَثَلُ کِفَّتَیِ الْمِیزَان
Example of a believer is like a plates of a balance( scale)« کُلَّمَا زِیدَ فِی‏ إِیمَانِهِ‏ زِیدَ فِی بَلَائِه
Whenever he increases in his faith Test and exams becomes more for him.
Therefore we should ask Allah of oh Allah ! Test us as long as we can bear it!

Please this Ayat from Sura Baqra which we recite in our Qunoot also:

لَا يُكَلِّفُ اللَّهُ نَفْسًا إِلَّا وُسْعَهَا لَهَا مَا كَسَبَتْ وَعَلَيْهَا مَا اكْتَسَبَتْ رَبَّنَا لَا تُؤَاخِذْنَا إِن نَّسِينَا أَوْ أَخْطَأْنَا رَبَّنَا وَلَا تَحْمِلْ عَلَيْنَا إِصْرًا كَمَا حَمَلْتَهُ عَلَى الَّذِينَ مِن قَبْلِنَا رَبَّنَا وَلَا تُحَمِّلْنَا مَا لَا طَاقَةَ لَنَا بِهِ وَاعْفُ عَنَّا وَاغْفِرْ لَنَا وَارْحَمْنَا أَنتَ مَوْلَانَا فَانصُرْنَا عَلَى الْقَوْمِ الْكَافِرِينَ

Allah does not impose upon any soul a duty but to the extent of its ability; for it is (the benefit of) what it has earned and upon it (the evil of) what it has wrought: Our Lord! do not punish us if we forget or make a mistake; Our Lord! do not lay on us a burden as Thou didst lay on those before us, Our Lord do not impose upon us that which we have not the strength to bear; and pardon us and grant us protection and have mercy on us, Thou art our Patron, so help us against the unbelieving people.(2:286)