A mobile container system comprising a first and a second standard-sized container releasibly securable together, by arranging the respective containers in parallel in a longer direction, each container comprising a cuboid metal frame with standard-sized corners, the respective containers being attached to each other and further comprising reinforcement beams to provide structural strength, wherein the respective containers are secured to each other via locking means arranged between at least one standard-sized corner or reinforcement beam of the first container and corresponding standard-sized corner or reinforcement beam of the second container, further wherein at least a portion of side walls of the respective containers, facing each other, are removed to provide enlarged interior space extending at least partially over both containers, the mobile container system being a mobile test unit system, wherein the portion of the side walls are removed to provide enlarged interior operating space as a test room extending over both containers, and the mobile test unit system further comprising a vehicle component exchangably arranged within the test room, and the mobile container system is configured to provide fire protected enlarged interior.