test: optimize expression unit test (#14102)
test: optimize expression unit test (#14102)


ming-relax/tidb,pingcap/tidb,EvilMcJerkface/tidb,pingcap/tidb,pingcap/tidb,XuHuaiyu/tidb,c4pt0r/tidb,ngaut/tidb,pingcap/tidb,Cofyc/tidb,ming-relax/tidb,c4pt0r/tidb,pingcap/tidb,coocood/tidb,kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,ngaut/tidb,kyle-wang/tidb,Cofyc/tidb,coocood/tidb,ngaut/tidb,c4pt0r/tidb,kyle-wang/tidb,pingcap/tidb,EvilMcJerkface/tidb,XuHuaiyu/tidb,c4pt0r/tidb,kyle-wang/tidb,ngaut/tidb,kyle-wang/tidb,c4pt0r/tidb,kyle-wang/tidb,ngaut/tidb