Fixed lint issues and missing documentation

internal/mock/findATender/catalog.go

@@ -168,6 +168,8 @@ func (c *Catalog) resolveOne(key string) *ocds.Classification {
 	return nil
 }
 
+// resolve returns copies of the classifications with keys, skipping keys
+// that have none.
 func (c *Catalog) resolve(keys []string) []ocds.Classification {
 	var out []ocds.Classification
 	for _, k := range keys {