@Test
public void testFromJson() {

    assertNull("should be null if either prefix and uri are missing",
            JcrNs.fromJson(JsonValue.EMPTY_JSON_OBJECT));
    assertNull("should be null prefix is missing",
            JcrNs.fromJson(key(KEYS.prefix(), prefix).get()));
    assertNull("should be null if uri is missing",
            JcrNs.fromJson(key(KEYS.uri(), uri).get()));
    JcrNs complete = JcrNs.fromJson(key(KEYS.prefix(), prefix).key(KEYS.uri(), uri).get());
    assertNotNull("complete should not be null", complete);
    assertEquals("complete prefix should be", prefix, complete.getPrefix());
    assertEquals("complete prefix should be", uri, complete.getUri());
}