fix: correctly add prepend default validators re: #14070

Author: vkarpov15

lib/schemaType.js

@@ -60,17 +60,7 @@ function SchemaType(path, options, instance) {
 
   for (const option of defaultOptionsKeys) {
     if (option === 'validate') {
-      const defaultValidators = Array.isArray(defaultOptions.validate)
-        ? defaultOptions.validate
-        : defaultOptions.validate == null
-          ? []
-          : [defaultOptions.validate];
-      const specifiedValidators = Array.isArray(options.validate)
-        ? options.validate
-        : options.validate == null
-          ? []
-          : [options.validate];
-      options.validate = [...defaultValidators, ...specifiedValidators];
+      this.validate(defaultOptions.validate);
     } else if (defaultOptions.hasOwnProperty(option) && !Object.prototype.hasOwnProperty.call(options, option)) {
       options[option] = defaultOptions[option];
     }

test/schematype.test.js

@@ -212,8 +212,9 @@ describe('schematype', function() {
     class TestSchemaType extends mongoose.SchemaType {}
     TestSchemaType.set('validate', v => typeof v === 'string');
 
-    const schemaType = new TestSchemaType();
-    schemaType.validate(v => v.length === 2);
+    const schemaType = new TestSchemaType('test-path', {
+      validate: v => v.length === 2
+    });
 
     let err = schemaType.doValidateSync([1, 2]);
     assert.ok(err);