static MetricsConfig create(String prefix) {
    return loadFirst(prefix, "hadoop-metrics2-" +
        StringUtils.toLowerCase(prefix) + ".properties", DEFAULT_FILE_NAME);
  }
@Test public void testCommon() throws Exception {
    String filename = getTestFilename("test-metrics2");
    new ConfigBuilder()
        .add("*.foo", "default foo")
        .add("p1.*.bar", "p1 default bar")
        .add("p1.t1.*.bar", "p1.t1 default bar")
        .add("p1.t1.i1.name", "p1.t1.i1.name")
        .add("p1.t1.42.bar", "p1.t1.42.bar")
        .add("p1.t2.i1.foo", "p1.t2.i1.foo")
        .add("p2.*.foo", "p2 default foo")
        .save(filename);

    MetricsConfig mc = MetricsConfig.create("p1", filename);
    LOG.debug("mc:"+ mc);

    Configuration expected = new ConfigBuilder()
        .add("*.bar", "p1 default bar")
        .add("t1.*.bar", "p1.t1 default bar")
        .add("t1.i1.name", "p1.t1.i1.name")
        .add("t1.42.bar", "p1.t1.42.bar")
        .add("t2.i1.foo", "p1.t2.i1.foo")
        .config;

    assertEq(expected, mc);

    testInstances(mc);
  }