The Chassis dynamometer comes closest to testing an engine in an automobile under real road conditions, in a laboratory itself. The automobile is mounted on a chassis such that its rear (driving) wheels are supported on a traction wheel and the front wheels are fixed on the ground using chocks. The traction wheels in contact exert a friction similar to that which is experienced on the road. The engine becomes loaded as the car wheels drive the traction wheels.
In actual driving, wind resistance and turning form part of the load, which are not incorporated in the test. However the traction wheels can be subjected to extra braking to include effects of grade.