util: migrate test-infra to testify for selector_test.go (#33505)
util: migrate test-infra to testify for selector_test.go (#33505)

close pingcap/tidb#33460
c4pt0r/tidb,pingcap/tidb,c4pt0r/tidb,kyle-wang/tidb,kyle-wang/tidb,pingcap/tidb,ngaut/tidb,kyle-wang/tidb,ngaut/tidb,pingcap/tidb,pingcap/tidb,ngaut/tidb,kyle-wang/tidb,c4pt0r/tidb,c4pt0r/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,ngaut/tidb,c4pt0r/tidb,ngaut/tidb,kyle-wang/tidb,ngaut/tidb,pingcap/tidb