This is a question that many Christians have not thought about and perhaps those that have thought of it might not have really understood it. There is a great difference between a tempt and a test. To tempt simply means to entice someone to do evil or wrong, the main purpose of a tempt is to see someone fall, it is hitting on the weak point of man by presenting something pleasurable or a gain to see that he falls but a test is a critical examination, observation or evaluation.
A test is a basis of evaluation or assessment to see your standing or how well you have done, that is why at the end of every semester in schools teachers give a test or exam to assess if the students properly understood what was thought, the purpose here is to see how well the student will do and to make him know his stand academically and not to make him fail.
God does not tempt, he tests because temptation is evil and God is righteous the bible made it clear in James 1:13(NASB) Let no one say when he is tempted, "I am being tempted by God"; for God cannot be tempted by evil, and He Himself does not tempt anyone. He does not entice anyone to do wrong because it is not his plan to see His creation (Man) fail.
He cannot tempt because if He does no man can overcome it because He knows every man inside out, He knows our weaknesses and therefore cannot entice us with evil. Genesis 22:1(NASB) now it came about after these things, that God tested Abraham, and said to him, "Abraham!" And he said, "Here I am." God tests a man so the man will see his standing and weigh himself so he could make any necessary adjustment. A test can either be passed or failed, a good student after passing a class test rejoices in the fact that he has learnt well but if he fails he realizes that he has not learned enough and he puts effort to learn properly so he does not fail the next time. When God tests man He places man in a scale.
Many people then ask if God does not tempt why then does He allow temptation come our way, it is true that He does not tempt but He permits temptation like He permitted the devil to tempt Job and Jesus. 1 Corinthians 10:13(NASB) No temptation has overtaken you but such as is common to man; and God is faithful, who will not allow you to be tempted beyond what you are able, but with the temptation will provide the way of escape also, so that you will be able to endure it. God allows us to be tempted because He knows we can overcome and give Him praise and He is not a wicked God that will allow a temptation that is mightier than us come our way.
He is a faithful God and understands our different levels and faith in our work with Him and He is able to carry us through temptations. He allows the devil tempt us so the devil will be put to shame and to make us realize our victory in Christ Jesus. Now there is a difference when God allows temptations come our way and when we look for temptations our way, for example in the case of lust. And at this point we Christians should not blame on God when we fall because we sought to be tempted because it is not Him who permitted it.
God is the tester that checks if you are active or inactive, dead or alive in faith, He checks your standing, devil is the tempter that wants to see your downfall so he would mock your faith and God.