docstr: Method：
  1. create a collection with partition key on multi fields
  2. verify the error raised
docstr_tok: ["Method\uff1a","1.","create","a","collection","with","partition","key","on","multi","fields","2.","verify","the","error","raised"]
code: def test_partition_key_on_multi_fields(self):
      """
      Method：
      1. create a collection with partition key on multi fields
      2. verify the error raised
      """
      self._connect()
      # both defined in field schema
      pk_field = cf.gen_int64_field(name="pk", is_primary=True)
      int64_field = cf.gen_int64_field(is_partition_key=True)
      string_field = cf.gen_string_field(is_partition_key=True)
      vector_field = cf.gen_float_vec_field()
      err_msg = "Expected only one partition key field"
      schema = cf.gen_collection_schema(
          fields=[pk_field, int64_field, string_field, vector_field],
          auto_id=True,
          check_task=CheckTasks.err_res,
          check_items={"err_code": 2, "err_msg": err_msg},
      )
  
      # both defined in collection schema
      err_msg = "Param partition_key_field must be str type"
      int64_field = cf.gen_int64_field()
      string_field = cf.gen_string_field()
      schema = cf.gen_collection_schema(
          fields=[pk_field, int64_field, string_field, vector_field],
          partition_key_field=[int64_field.name, string_field.name],
          auto_id=True,
          check_task=CheckTasks.err_res,
          check_items={"err_code": 2, "err_msg": err_msg},
      )
  
      # one defined in field schema, one defined in collection schema
      err_msg = "Expected only one partition key field"
      int64_field = cf.gen_int64_field(is_partition_key=True)
      string_field = cf.gen_string_field()
      schema = cf.gen_collection_schema(
          fields=[pk_field, int64_field, string_field, vector_field],
          partition_key_field=string_field.name,
          auto_id=True,
          check_task=CheckTasks.err_res,
          check_items={"err_code": 2, "err_msg": err_msg},
      )
  
imports: import pytest
  from base.client_base import TestcaseBase
  from common import common_func
  from common import common_type
  from common.common_type import CaseLabel, CheckTasks
  from utils.util_pymilvus import *
label_desc: Use image node_id 5 for calling the TestPartitionKeyInvalidParams obj's underlying member method code with example usage: obj.test_partition_key_on_multi_fields() without return types