A way to test the vaidity of a religion. What would happen if their valued texts had never been written? Suppose the Torah, New Testament and Koran were not in existence. How would these religions know about their God?
If the Torah had never been written one would never know about Moses. One could however know God / Yahweh without the Torah in the same manner that Abraham knew God without any text or book.
If the Koran had never been written one would never know about Mohammed. One could however know God / Al-Lah from his creation in a similar way to Abraham.
If the New Testament had never been written one would never know about Jesus. As Christians worship Jesus as God then one could never get to know this God. You can't know Jesus as God without a New Testament.
It each of the above religions the texts point to God. In each of the religions fundamentalists have interpreted the texts wrongly and made their intepretation of the texts absolutes.