My regular md told me there is no test to see if I have psoriasis but reading answers here, I see you can do a biopsy test. What is true?

Both in a way. Your doctor is correct. There is no specific test for psoriasis. The diagnosis is usually based on history and physical exam. In atypical cases or if the diagnosis is not clear a biopsy may be done to rule out other conditions. Other than that, there are no specific tests to confirm or exclude this diagnosis.