executor: migrate test-infra to testify for metrics_reader_test.go (#32452)
executor: migrate test-infra to testify for metrics_reader_test.go (#32452)

close pingcap/tidb#28598
pingcap/tidb,kyle-wang/tidb,kyle-wang/tidb,c4pt0r/tidb,c4pt0r/tidb,pingcap/tidb,c4pt0r/tidb,pingcap/tidb,kyle-wang/tidb,c4pt0r/tidb,pingcap/tidb,kyle-wang/tidb,ngaut/tidb,ngaut/tidb,c4pt0r/tidb,pingcap/tidb,ngaut/tidb,ngaut/tidb,kyle-wang/tidb,ngaut/tidb,kyle-wang/tidb,pingcap/tidb,ngaut/tidb,c4pt0r/tidb