Error message when testing memberships: "Expected one PaymentProcessor but found 0"
I had the same error. It appeared that we had removed a payment processor that we had used before, but don’t use any more (never do that. Just disable the payment processor).
When searching for memberships, also attached payments are displayed. Some of these payments het the removed payment processor. The was causing the error.
We restored the payment processor. In the database we changed the ID’s of the live and the test payment processor to the original ID’s. That solved the issue.