Aptitude and ability tests are designed to assess your intellectual performance. These types of test can be broadly classified onto the groups shown and you may be asked to sit a test which consists only of ‘numerical’ questions or these may form part of a test which consists of questions of different types.
Recruitment and selection tests are only part of the selection process and you will still be asked to complete an application form, send in a copy of your resume and attend at least one interview. All of these things will tell the employer something about you and help them to choose the most appropriate candidate for the vacancy. Recruitment and selection tests can be split into personality tests and aptitude/ability tests.
The principle behind personality tests is that it is possible to quantify your personality characteristics by asking you about your feelings, thoughts and behavior. Personality has a significant role to play in deciding whether you have the enthusiasm and motivation that the employer is looking for and whether you going to fit in to the organization, in terms of your personality, attitude and general work style? Personality tests can be applied in a straightforward way at the early stages of selection to screen-out candidates who are likely to be unsuitable for the job.
Reference: http://www.psychometric-success.com/faq/faq-recruitment-and-selection-tests.htm