Document how to test the behavior of equals() itself.
RELNOTES=n/a
@@ -176,6 +176,12 @@ public class Subject<S extends Subject<S, T>, T> {
* <li>they are boxed integer types ({@code Byte}, {@code Short}, {@code Character}, {@code
* Integer}, or {@code Long}) and they are numerically equal when converted to {@code Long}.
* </ul>
+ *
+ * <p><b>Note:</b> This method does not test the {@link Object#equals} implementation itself; it
+ * <i>assumes</i> that method is functioning correctly according to its contract. Testing an
+ * {@code equals} implementation requires a utility such as <a
+ * href="https://mvnrepository.com/artifact/com.google.guava/guava-testlib">guava-testlib</a>'s <a
+ * href="https://static.javadoc.io/com.google.guava/guava-testlib/23.0/com/google/common/testing/EqualsTester.html">EqualsTester</a>.
*/
/*
* TODO(cpovirk): Possibly ban overriding isEqualTo+isNotEqualTo in favor of a
