@Test
    void throwAuthenticationExceptionIfDoAuthenticateReturnsNull() {
        assertThrows(AuthenticationException.class, () -> {
            abstractAuthenticator = createAuthcReturnNull();
            abstractAuthenticator.authenticate(newToken());
        });
    }
Ensures that the authenticate() method throws an AuthenticationException if the subclass returns <tt>null</tt>
as the return value to the doAuthenticate() method.
core/src/test/java/org/apache/shiro/authc/AbstractAuthenticatorTest.java