Which statement is true if a test has known validity?

A test having known validity means that it accurately measures what it purports to measure—that is, the construct it is designed to assess. Validity encompasses several aspects, including content validity, criterion-related validity, and construct validity. Therefore, when it is stated that a test has known validity, it confirms that the test effectively captures the construct it was intended to measure, aligning with the claims made by its publishers.

In the context of the other options, while factors such as test/retest reliability and suitability for diverse populations are important considerations for a comprehensive understanding of a test's effectiveness, they do not directly relate to the definition of validity. A test can have established reliability without necessarily possessing validity, and just because a test fits a certain population does not guarantee it will measure the intended construct accurately. Consequently, the assertion that a test measures what its publishers claim is the most accurate and pertinent statement regarding its known validity.