Testing device for testing the tightness of a weld joint connecting several cables to a cable bundle, comprising - a first test chamber wall element which has a first test chamber part on its chamber-side broad side; - a second test chamber wall element which has a second test chamber part on its chamber-side broad side, wherein the test chamber wall elements (5, 6) and their test chamber parts (10, 14) face each other and correspond with each other to form a test chamber; - an adjustment device by means of which the testing device is adjustable between an insertion position, in which the test chamber is open for inserting or removing the weld joint, and a test position, in which the test chamber wall elements (5, 6) and their test chamber parts (10, 14) are tensioned towards each other, whereby the test chamber is closed; - a test pressure connection which opens at its chamber-side end into one of the test chamber parts (10, 14) and whose other end can be fluidically connected to a pressure testing device; - a cable feed-through corresponding to the cables of the cable bundle, which is designed to fix the cables in the test position; wherein in the test position the test chamber and an environment of the test chamber are fluidically sealed from each other via the cable feed-through when the weld joint is arranged in the test chamber and the cables of the cable bundle are led out of the test chamber through the cable feed-through, wherein the cable feed-through is formed from a first cable feed-through element held on the first test chamber wall element and a second cable feed-through element held on the second test chamber wall element, characterized in that each cable feed-through element (22, 23) has grooves corresponding to the cables of the cable bundle into which the cables can be inserted. - a first test chamber wall element which has a first test chamber part on its chamber-side broad side; - a second test chamber wall element which has a second test chamber part on its chamber-side broad side, wherein the test chamber wall elements (5, 6) and their test chamber parts (10, 14) face each other and correspond with each other to form a test chamber; - an adjustment device by means of which the testing device is adjustable between an insertion position, in which the test chamber is open for inserting or removing the weld joint, and a test position, in which the test chamber wall elements (5, 6) and their test chamber parts (10, 14) are tensioned towards each other, whereby the test chamber is closed; - a test pressure connection which opens at its chamber-side end into one of the test chamber parts (10, 14) and whose other end can be fluidically connected to a pressure testing device; - a cable feed-through corresponding to the cables of the cable bundle, which is designed to fix the cables in the test position; wherein in the test position the test chamber and an environment of the test chamber are fluidically sealed from each other via the cable feed-through when the weld joint is arranged in the test chamber and the cables of the cable bundle are led out of the test chamber through the cable feed-through, wherein the cable feed-through is formed from a first cable feed-through element held on the first test chamber wall element and a second cable feed-through element held on the second test chamber wall element, characterized in that each cable feed-through element (22, 23) has grooves corresponding to the cables of the cable bundle into which the cables can be inserted.