@Test
  public void testOnlySetMetaWALProvider() throws IOException {
    Configuration conf = new Configuration();
    conf.set(META_WAL_PROVIDER, WALFactory.Providers.asyncfs.name());
    WALFactory walFactory = new WALFactory(conf, this.currentServername.toString());
    assertEquals(WALFactory.Providers.defaultProvider.clazz,
      walFactory.getWALProvider().getClass());
    assertEquals(WALFactory.Providers.asyncfs.clazz, walFactory.getMetaProvider().getClass());
  }
A loaded WAL coprocessor won't break existing WAL test cases.
hbase-server/src/test/java/org/apache/hadoop/hbase/wal/TestWALFactory.java