These tests are designed to assess an individual's innate or learned level of competence to undertake a particular task or work, at a given level.
A variety of tests, including ability tests are developed for this purpose where in the context of work, a particular competence is desired in a given area. For example, for an Accountant, individuals may be asked to complete a 'numerical' aptitude test.
The difference between Aptitude and Ability may be argued to be the same as that between nature and nurture. Aptitude indicates one's potential or preference to doing a task, where ability looks at where they are able to do this. For example, for an Accountancy job, you may not be too keen on employing somebody who has a preference for a high-level attention to detail. In Accountancy, a strong preference for high attention to detail is desirable given such an analytical job.
For more information, see our section on 'Ability tests'.