@Test
    public void testMissingFieldsFacebook() {
        val client = new FacebookClient(KEY, SECRET);
        client.setCallbackUrl(CALLBACK_URL);
        client.setFields(null);
        TestsHelper.initShouldFail(client, "fields cannot be blank");
    }
This class tests the {@link OAuth20Client} class.

@author Jerome Leleu
@since 1.0.0
pac4j-oauth/src/test/java/org/pac4j/oauth/client/OAuth20ClientTests.java