private String[] switchExpectedCoprocessors(String[] expectedCoprocessors) {
    if (Arrays.equals(regionServerSystemCoprocessors, expectedCoprocessors)) {
      expectedCoprocessors = masterRegionServerSystemCoprocessors;
    } else {
      expectedCoprocessors = regionServerSystemCoprocessors;
    }
    return expectedCoprocessors;
  }
return the subset of all regionservers (actually returns set of ServerLoads) which host some
region in a given table. used by assertAllRegionServers() below to test reporting of loaded
coprocessors.
@param tableName : given table.
@return subset of all servers.
hbase-endpoint/src/test/java/org/apache/hadoop/hbase/coprocessor/TestClassLoading.java