@Test
public void testStreamNsPrefix() {

    assertEquals("empty string means empty stream",
            0, JsonCnd.streamNsPrefix("").count());
    assertEquals("colonless string means empty stream",
            0, JsonCnd.streamNsPrefix("foo").count());
    assertEquals("colon string means single prefix",
            1, JsonCnd.streamNsPrefix("nt:foo").count());
    assertEquals("colon string means captured prefix",
            "nt", JsonCnd.streamNsPrefix("nt:foo").findFirst().orElse(""));
    assertEquals("double-colon string still means single prefix",
            1, JsonCnd.streamNsPrefix("nt:foo:bar").count());
    assertEquals("double-colon string still means captured prefix",
            "nt", JsonCnd.streamNsPrefix("nt:foo:bar").findFirst().orElse(""));
}