### Question:
DataNode { public static boolean isValidDataNode(final String dataNodeStr) { return dataNodeStr.contains(DELIMITER) && 2 == Splitter.on(DELIMITER).splitToList(dataNodeStr).size(); } DataNode(final String dataNode); static boolean isValidDataNode(final String dataNodeStr);  }### Answer:
@Test public void assertIsValidDataNode() { assertTrue(DataNode.isValidDataNode("ds_0.tbl_0")); }
@Test public void assertIsInvalidDataNodeWithoutDelimiter() { assertFalse(DataNode.isValidDataNode("ds_0_tbl_0")); }
@Test public void assertIsInvalidDataNodeWithTwoDelimiters() { assertFalse(DataNode.isValidDataNode("ds_0.tbl_0.tbl_1")); }