types: improve test coverage in types/json (#9697)
types: improve test coverage in types/json (#9697)


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