Testimonies Don't Have to Be Provable - or Even Accurate - to Be Valid

Testimony has the same root as testament and testify - which are legal terms for an official record and to make an official statement. Thus, a testimony can be about absolutely anything and is nothing more than saying, writing, or doing something in an official manner that reflects whatever is said. "I know" - "I believe" - I feel" - "I saw (witnessed)" - "I assume" - etc. all are legitimate forms of testimony - and the only false testimonies are ones that are not consistent with the belief of the person providing it  - or, to say it more clearly, the ones that the testifier knows to be inaccurate.

For example, if a witness in a trial says, "I know . . ." that person is unable to be charged with perjury even if it turns out that they are wrong (meaning they didn't know what they claimed to know), as long as it is believed that they were sincere in their expression of knowledge.

Thus, spiritual experiences are a perfectly acceptable foundation for religious testimonies, whether what is believed is true or not, objectively - or, in many cases, inadequate to prove accuracy in an objective way. After all, most people base what they believe or believe they know on what they feel, to one degree or another.