Dear Member,
Designing job aptitude tests requires studying the job extensively. While general aptitude tests can be conducted, customized tests better suit job requirements. However, creating these tests may require hiring psychologists unless you prefer "free" resources. The previous member has provided a few links to free tests.
From the internet, you can get free aptitude tests. However, the internet is available to all, including employers and job aspirants. If employers use web resources to design aptitude tests, and candidates also use the same resources, then the candidates will be well-prepared for the tests. In that case, will it not diminish the test's value? Please consider this point.
Thanks,
Dinesh Divekar