@Test
public void testExistingField() {

    InternalEvent ievent = new InternalEvent("foo", null, 1);
    JsonObject actualJsonObject = new JsonObject();
    actualJsonObject.addProperty("ex", "exists");
    GenericJsonEvent jsonEvent = new GenericJsonEvent(actualJsonObject);
    ievent.setEventObj(jsonEvent);
    DeleteFieldOperation operation = new DeleteFieldOperation("ex");
    operation.perform(ievent);
    JsonObject expectedJsonObject = new JsonObject();
    assertEquals(expectedJsonObject, actualJsonObject);
}