write some testz

src/metabase/driver/mongo.clj

src/metabase/driver/mongo/query_processor.clj

src/metabase/driver/mongo/util.clj

src/metabase/driver/query_processor.clj

src/metabase/models/field.clj

test/metabase/driver/query_processor_test.clj

test/metabase/test/data.clj

test/metabase/test/util/mql.clj