an instrument or systematic procedure for measuring a sample of behavior.
(Gronlund, Norman E.. and Robert L. Linn. Measurement and evaluation in teaching. 6th ed. New York, Macmillan, 1990, p. 5.)
deals with the development, validation, administration, scoring, and interpretation of psychological tests. Psychological tests are defined as standardized, repeatable procedures used to elicit and measure samples of human behavior. ...Because testing involves measurement, tests have procedures for coding, scoring, or quantifying the behavior that is elicited so that it can be compared with normative data systematically collected on similar samples. Testing is used to evaluate (1) human abilities, including intelligence, aptitudes, skills, and achievement in various areas; (2) personality characteristics, which include traits, attitudes, interests, and values; and (3) adjustment and mental health, which involves detecting signs and symptoms of psychological and neurological disorders and appraising the effectiveness of psychological functioning.
(Kazdin, Alan E. Encyclopedia of psychology. Washington, D.C., American Psychological Association, 2000, vol. 8, p. 47-48.)