Welding Certifications And Training
A welding certification is technically a procedure or a welder qualification test. If you have the skill level and follow the directions then you should produced the same results as the procedure specifies.
By comparison it's no different than following a recipe. If you use the ingredients as specified and cook by following the instructions you will get the desired results wanted! In this case instead of making a cheese burger you are making a sound quality welded joint.
The main difference between a welding certification and a welder qualification test is that it is certified by an organization and it will be supervised by someone who completed the appropriate training who has been approved by that organization to oversee that procedure.