A test tape device is disclosed herein for use with a replaceable analytical tape cassette, where the device includes a housing having a cassette compartment covered by a cassette door and a housing opening for sample application, a protective cover that can be moved between a closed position covering the housing opening and a release position allowing access to the housing opening and a door lock for retaining the cassette door in the closed position, wherein the protective cover is coupled with the door lock via an interlocking mechanism, such that the door lock can only be unlocked in the release position of the cover.