The Lemon Test is a three-step process to check if a law violates the First Amendment of the U.S. Constitution, according to the National Paralegal College. Its questions ask if a law has a secular purpose, is designed to enhance or inhibit religion or excessively mixes government and religion.
The National Paralegal College reports that the test was first introduced during a 1970 U.S. Supreme Court case, Lemon v. Kurtzman. The Establishment Clause of the Constitution dictates that Congress is prohibited from passing any law respecting an establishment of religion, often known as the separation of church and state. If a law is determined to have a non-secular purpose, enhance or inhibit religion, or mix government and religion, then it fails the test and violates the clause.