Tests and scales are referenced by their supporting  literature such as the manual. The reference will then depend on the format of the supporting literature, which is often a authored or edited book or a journal article.

Author. INITIALS. (Year). Title of test: Subtitle (Test code): Technical Manual. Publisher

Weschler, D., & Naglieri, J, A. (2006). Wechsler Nonverbal Scale of Ability (WNV): Technical manual. Pearson

Wechsler Nonverbal Scale of Ability
WNV
David Wechsler, PhD 
Jack A. Naglieri, PhD
2006

If supporting literature is not available then you can reference the test itself

Author, INITIALS. (Year). Title of test: Subtitle.  URL (if accessed online)

Weschler, D., & Naglieri, J, A. (2006). Wechsler Nonverbal Scale of Ability (WNV). Pearson

If you are using the information provided about a test given on the database record describing the test (such as in PsycTESTS) cite the database record itself

Author, INITIALS. (Year). Title of  the Test Database Record [Database Record]. Test Database Name. URL

Weschler, D., & Naglieri, J, A. (2006). Wechsler Nonverbal Scale of Ability (WNV). [Database record] PsycTESTS. URL

In-text Citations: Follows standard Author/Year format - For further guidance see the In-Text Citations page