It can be compared with a subjective test, which is evaluated by giving an opinion, usually based on agreed criteria. Objective tests are popular because they are easy to prepare and take, quick to mark, and provide a quantifiable and concrete result.
For example
True or false questions based on a text can be used in an objective test.
In the classroom
Marking objective tests together in the class is a useful way to exploit them further as it gives the learners the opportunity to discuss answers, try to justify choices, and help each other etc.
See also:
https://www.teachingenglish.org.uk/article/achievement-test
https://www.teachingenglish.org.uk/article/criterion-referenced-test
https://www.teachingenglish.org.uk/article/diagnostic-test
https://www.teachingenglish.org.uk/article/norm-referenced-test
https://www.teachingenglish.org.uk/article/proficiency-test
https://www.teachingenglish.org.uk/article/subjective-test
Further links:
https://www.teachingenglish.org.uk/article/assessment
https://www.teachingenglish.org.uk/article/testing-assessment
https://www.teachingenglish.org.uk/article/test-writing
https://www.teachingenglish.org.uk/article/test-question-types