Test device comprises a test tape (16) having a functional section (40) that can be brought into a functional position by advancing the tape. An independent claim is also included for a tape cassette for the test device. Preferred Features: The functional section interacts with a measuring unit (18) in the functional position. The functional section has a calibrating field for calibrating the measuring unit. The functional section has a white, black, gray, colored or transparent calibrating field for an optical measuring unit. A comparator (42) is also provided for comparing a measured value determined on an unused test section (38) or functional section with a theoretical value.
