static String pigSchemaToString(Schema pigSchema) {
    final String pigSchemaString = pigSchema.toString();
    return pigSchemaString.substring(1, pigSchemaString.length() - 1);
  }
@Test
  public void testSchemaEvolution() {
    Map<String, Set<String>> map = new LinkedHashMap<String, Set<String>>();
    map.put(
        "pig.schema",
        new LinkedHashSet<String>(Arrays.asList(
            "a:int, b:int, c:int, d:int, e:int, f:int", "aa:int, aaa:int, b:int, c:int, ee:int")));
    Schema result = getPigSchemaFromMultipleFiles(
        new MessageType("file_schema", new PrimitiveType(OPTIONAL, INT32, "a")), map);
    assertEquals("a: int,b: int,c: int,d: int,e: int,f: int,aa: int,aaa: int,ee: int", pigSchemaToString(result));
  }