@Test
  public void testOnlySetWALProvider() throws IOException {
    Configuration conf = new Configuration();
    conf.set(WAL_PROVIDER, WALFactory.Providers.multiwal.name());
    WALFactory walFactory = new WALFactory(conf, this.currentServername.toString());
    // class of WALProvider and metaWALProvider are the same when metaWALProvider is not set
    assertEquals(WALFactory.Providers.multiwal.clazz, walFactory.getWALProvider().getClass());
    assertEquals(WALFactory.Providers.multiwal.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