test: fix tests

Author: vkarpov15

lib/schema/SubdocumentPath.js

@@ -340,6 +340,14 @@ SubdocumentPath.defaultOptions = {};
 
 SubdocumentPath.set = SchemaType.set;
 
+/*!
+ * ignore
+ */
+
+SubdocumentPath.prototype.toJSON = function toJSON() {
+  return { path: this.path, options: this.options };
+};
+
 /*!
  * ignore
  */