A test device for a plug-in connection is configured to detect one or more of moisture and liquid in at least one protective chamber of the plug-in connection. The plug-in connection has a first plug part and a second plug part each with a plurality of electrically conductive contact elements. The first and second plug parts are configured to be plugged together such that at least some of the contact elements of the first plug part come into electrical contact with at least some contact elements of the second plug part. The first and second plug parts, when in the plugged-together state, form the at least one protective chamber, which is configured for the contact elements. In one embodiment, the plug-in connection is associated with a control unit of a steering system for a motor vehicle.