"Testrone" here seems to be a misspelling of "testorne" - "testorne" itself is a variant of "tester," a type of sixpence in use in England from the time of Henry VIII. The tester itself was based on the "teston," a coin in use in various European locales in the 16th century. The teston was originally worth 12 pence, but quickly devalued to 6 and subsequently recalled, though they remained unofficially in circulation into the 17th century. (All information gleaned from OED.)