A testing device for a xDSL distribution unit of a telecommunication system, the testing device being configured to be plugged into a functional element of the xDSL distribution unit, the testing device comprising a contact tongue section through which the testing device can be plugged into the functional element, the functional element of the xDSL distribution unit having at least three contact elements (12.1, 12.2, 12.3) with cutting contacts being configured to connect a wire to the respective contact element, namely the first contact element (12.1) to which a wire carrying a voice signal can be connected, the second contact element (12.2) to which a wire carrying a data signal can be connected and the third contact element (12.3) to which a wire carrying a line signal being a combined voice and data signal can be connected, the contact tongue section having at a first side or upper side of the contact tongue section four contact sections (A1, A2, A3, A4), and at a second side or lower side of the contact tongue section two contact sections (B1, B2), wherein a first and a third contact section (A1, A3) provided at the first side or upper side of the contact tongue section are both electrically connected to a fifth contact section provided at the second side or lower side of the contact tongue section, wherein a second and a fourth contact section (A2, A4) provided at the first side or upper side of the contact tongue section are both electrically connected to a sixth contact section provided at the second side or lower side of the contact tongue section, wherein when the testing device is plugged into the functional element of the xDSL distribution unit from a first side of the functional element in a first orientation of the testing device, the testing device electrically connects the first and second contact elements (12.1, 12.2) of the functional element, wherein when the testing device is plugged into the functional element of the xDSL distribution unit from the first side of the functional element in a second orientation of the testing device, the testing device electrically connects the second and third contact elements (12.2, 12.3) of the functional element. the testing device being configured to be plugged into a functional element of the xDSL distribution unit, the testing device comprising a contact tongue section through which the testing device can be plugged into the functional element, the functional element of the xDSL distribution unit having at least three contact elements (12.1, 12.2, 12.3) with cutting contacts being configured to connect a wire to the respective contact element, namely the first contact element (12.1) to which a wire carrying a voice signal can be connected, the second contact element (12.2) to which a wire carrying a data signal can be connected and the third contact element (12.3) to which a wire carrying a line signal being a combined voice and data signal can be connected, the contact tongue section having at a first side or upper side of the contact tongue section four contact sections (A1, A2, A3, A4), and at a second side or lower side of the contact tongue section two contact sections (B1, B2), wherein a first and a third contact section (A1, A3) provided at the first side or upper side of the contact tongue section are both electrically connected to a fifth contact section provided at the second side or lower side of the contact tongue section, wherein a second and a fourth contact section (A2, A4) provided at the first side or upper side of the contact tongue section are both electrically connected to a sixth contact section provided at the second side or lower side of the contact tongue section, wherein when the testing device is plugged into the functional element of the xDSL distribution unit from a first side of the functional element in a first orientation of the testing device, the testing device electrically connects the first and second contact elements (12.1, 12.2) of the functional element, wherein when the testing device is plugged into the functional element of the xDSL distribution unit from the first side of the functional element in a second orientation of the testing device, the testing device electrically connects the second and third contact elements (12.2, 12.3) of the functional element. the contact tongue section having at a first side or upper side of the contact tongue section four contact sections (A1, A2, A3, A4), and at a second side or lower side of the contact tongue section two contact sections (B1, B2), wherein a first and a third contact section (A1, A3) provided at the first side or upper side of the contact tongue section are both electrically connected to a fifth contact section provided at the second side or lower side of the contact tongue section, wherein a second and a fourth contact section (A2, A4) provided at the first side or upper side of the contact tongue section are both electrically connected to a sixth contact section provided at the second side or lower side of the contact tongue section, wherein when the testing device is plugged into the functional element of the xDSL distribution unit from a first side of the functional element in a first orientation of the testing device, the testing device electrically connects the first and second contact elements (12.1, 12.2) of the functional element, wherein when the testing device is plugged into the functional element of the xDSL distribution unit from the first side of the functional element in a second orientation of the testing device, the testing device electrically connects the second and third contact elements (12.2, 12.3) of the functional element.