A diagnostic test is used to assess :

The correct answer is learners’ strong and weak points in language.

Explanation:

A diagnostic test in language learning and education is designed to identify a learner's specific strengths and weaknesses in a subject area or language skill.

Key features of a diagnostic test include:

1. Identifying Gaps: It pinpoints specific areas where a student excels or struggles, allowing teachers to tailor subsequent instruction and remedial measures.

2. Formative Purpose: Unlike achievement or summative tests (which rank students or measure overall learning outcome at the end of a course), diagnostic testing takes place to assess learning needs before or during the instructional process.

Therefore, assessing learners' strong and weak points in language is the primary function of a diagnostic test.