@Test public void testAtLeastOneFieldIsFilledExcludingIdAndOwner() throws JSONException { Child child = new Child("id1", "owner1", null); assertThat(child.isValid(), is(false)); child.put("test1", "value1"); assertThat(child.isValid(), is(true)); child.remove("test1"); assertThat(child.isValid(), is(false)); }