executor: migrate test-infra to testify for slow_query_test.go (#30521)
executor: migrate test-infra to testify for slow_query_test.go (#30521)

close pingcap/tidb#28615
ngaut/tidb,c4pt0r/tidb,kyle-wang/tidb,c4pt0r/tidb,pingcap/tidb,pingcap/tidb,kyle-wang/tidb,ngaut/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,ngaut/tidb,kyle-wang/tidb,kyle-wang/tidb,pingcap/tidb,ngaut/tidb,pingcap/tidb,ngaut/tidb,c4pt0r/tidb,kyle-wang/tidb,c4pt0r/tidb,ngaut/tidb,pingcap/tidb,c4pt0r/tidb