Run a Jest Test and validate the result is an array of errors?

Question

I am attempting to use the class-validator module to confirm my object is valid when using a Mapper code.

order.entity.ts

import {
  ArrayMinSize,
  IsArray,
  IsBoolean,
  IsDate,
  IsDateString,
  IsInt,
  IsOptional,
  IsString,
  ValidateNested,
} from 'class-validator';
import { Transform, Type } from 'class-transformer';

export class Order {
  @IsInt()
  @IsOptional()
  OrderId?: number;

  @IsString()
  @IsOptional()
  RetailerName?: string | null;

  @IsString()
  RetailerOrderId: string;

  @IsString()
  @IsOptional()
  Brand?: string | null;
}

I have a mapper set up as follows: data.mapper.ts

import { Order } from './entities/Order.entity';
import { transformAndValidate } from 'class-transformer-validator';

export class OrderMapper {
  public static async toDomainFromMessage(raw: any): Promise<Order> {
    const order = new Order();
    order.RetailerName =
      raw.source ??
      (() => {
        new Error('Retailer Name is missing');
      })();
    order.RetailerOrderId = raw.externalOrderId
      ? raw.externalOrderId.toString()
      : null;

    const result = await transformAndValidate(Order, order)
      .then((orderObject: Order) => {
        return orderObject;
      })
      .catch((err) => {
        throw err;
      });
    return result;
  }
}

I test by passing in an object like this

const order = {
  orderId: 12345678,
  shipping_country_code: 'US',
  orderTypes: [
    {
      orderTypeLabel: 'Wholesale',
      orderTypeId: '14',
    },
  ],
}; 

Since it is missing the ExternalOrder field, it throws an array of errors of type Validation Error.

I have tried catching the error using this code, but cannot figure out the expect command I need to use to verify I have some Validation Error objects within the caught error variable

try {
  const order = await OrderMapper.toDomainFromMessage(order);
} catch (e) {
  console.log(e);
}

Answer 1

You can use the Jest expect function with a custom matcher to verify that the caught error is an instance of the ValidationError class from the class-validator module, and that it contains the expected number of errors.

Add this code under the catch block.

expect(e).toHaveLength(length);
e.forEach((error) => {
  expect(error).toBeInstanceOf(ValidationError);
});