You cannot put God to the test
One apologetic defence against criticism of theism is to claim You cannot but God to the test, sometimes in reference to Luke 4:12 . This puts God beyond the reach of reliable observation, makes him unfalsifiable and therefore outside the bounds of knowledge. However, the Bible contains many examples of being put to the test. The question arises why was it ok then and not now?
- "No, you can't put God in a test tube and “prove” He exists the same way you can prove a chemical exists "
If one selects a experimental test procedure with an a priori determination to reject all evidence than its a bit self-defeating isn't it? Designing a scientific experiment to obtain evidence of God is an interesting concept, and one couldn't be assured of having a valid criterion for the selection of what is valid evidence without biasing the test.
Jesus did mention to Satan (Luke 4:1-13) "'YOU SHALL NOT PUT THE LORD YOUR GOD TO THE TEST".
So, creating test conditions for God implicitly is a bad choice. 
Biblical testing of God
The characters in the Bible seem to have no trouble in putting God to the test:
Some faith required
One explanation is that miracles only can occur among those with faith, rather than doubters.
- "It’s acceptable to “test” God in regard to tithes and offerings, for example, but unacceptable when the test is rooted in doubt. "
Apart from contradicting Biblical examples, this does not explain why miracles are not observed at all by reliable witnesses or produce any lasting evidence.
God would be testable if he exists
If God interacts with physical reality, the effects would be observable. A rational and benevolent being would also act in a consistent fashion. Therefore, God's interactions and effects would be repeatable. In a certain circumstances, God would always intervene. For instance, if God performed healing miracles, a particular type of person in a type of circumstance would always be healed (because it would be senseless and arbitrary for God to heal one and not the other). Give that we would expect God's actions to be repeatable, they would be subject to potential falsification.
Scientific studies attempting to find divine intervention have so far found nothing. For instance:
- Efficacy of prayer
- Christians being immune to snake bites or poisons. Mark 16:17-18
- Faith healing Mark 16:17-18
- Evaluating the accuracy of modern prophecy.
As far as we can tell, God does not interact with physical reality or does not exist. Since many mainstream religions are quite specific about how God intervenes in the world, this disproves most monotheistic religions.
The Dragon In My Garage
Thought experiments such as The Dragon In My Garage point out that an entity that cannot be disproved cannot be distinguished from a non-existent entity. Antony Flew argued that theological statements make no assertion as to what cannot possibly happen. Therefore, theological statements are not assertions because there is no evidence that could possibly refute them.
- "Take such utterances as "God has a plan," "God created the world," "God loves us as a father loves his children." [...] But let us confine ourselves to the cases where those who utter such sentences intend them to express assertions.[...] Now to assert that such and such is the case is necessarily equivalent to denying that such and such is not the case. [...] one way of trying to understand (or perhaps it will be to expose) his utterance is to attempt to find what he would regard as counting against, or as being incompatible with, its truth. [...] And if there is nothing which a putative assertion denies then there is nothing which it asserts either; and so it is not really an assertion. "
Material evidence cannot demonstrate God
- "Second, the scientific method, along with a materialistic worldview, necessarily excludes transcendence--that which exists independent of the universe. Therefore, it can't detect what is outside of the material realm since it is based on observing things inside the material realm. [...] Therefore, to ask for scienfically [sic] testable, material, non-transcendent based evidence for an immaterial, transcendent God is the wrong approach because it is a category mistake"
The scientific method can study anything material, as well as anything that interacts with the material world. Is the apologist really saying God does not interact with the material universe? If so, miracles including bodily resurrections, are impossible.