Types of Test and purpose: (When, What and How)

Beginning: Diagnostic and placement test / aptitude test 

Reason: It helps the teacher as well as the students to identify which areas to work on or to improve as the time goes by. 

During (Formative): Progressive Test

Reason: It helps to measure a learner's level of language.

End (Summative): Achievement Test

Reason: It helps to evaluate learners understanding on specific materials.