Each state sets separate laws regarding vehicle inspections, so some of the items tested vary. However, most states have criteria that determine whether the car is safe to operate. In some counties, emissions testing is required to ensure the car doesn't pollute the air beyond allowable limits.
In Texas, inspectors must make sure the driver has proof of insurance before looking at the car. As of 2015, there are 20 different points to the safety inspection, from the operation of the horn and windshield wipers to the functioning of turn signals and tail lights. For some cars, the inspector must test the gas cap to ensure it doesn't leak.
People who live in the El Paso, Williamson or Travis counties of Texas, as well as in the Dallas-Fort Worth and Houston/Galveston areas, have to get emissions testing done as part of the inspection, since these areas have air quality issues, and cars are not allowed to contribute more than a specified amount of air pollution.
In Ohio, the list of items on the safety inspection sheet is similar, such as the operation of the brakes, defroster, electrical system, horn, lights, odometer and tires. As of 2015, residents of seven specific counties have to undergo emissions testing as well. Checking inspection criteria in one's state of residence helps to ensure passing of the inspection.