Create a simulated constructor to generate an error

Question

Create a simulated constructor to generate an error

Currently, I am faced with a challenge of writing a test that is expected to fail when trying to instantiate the S3Client object. It seems like Vitest (similar to Jest) replaces the constructor with its own version when mocked, preventing my original constructor from being invoked.

Here is what I have tried:

vi.mock('@aws-sdk/client-s3', async () => {
  const module = await vi.importActual<typeof import('@aws-sdk/client-s3')>('@aws-sdk/client-s3')

  Object.defineProperty(module.S3Client.prototype, 'constructor', {
    value: function () {
      throw new Error("Can't construct S3Client")
    },
    writable: true,
    configurable: true,
  })

  return {
    ...module,
  }
})

Could anyone advise me on how to generate an exception from the constructor in this scenario?

javascript typescript jestjs vitest

Answer 1

Answer №1

If you're wondering how to achieve this using vitest, I'm not entirely sure. However, if you switch to jest, you might be able to implement something similar:

jest.mock('@aws-sdk/client-s3', () => {
  return {
    S3Client: jest.fn().mockImplementation(() => {
      throw new Error('constructor error');
    }),
  };
});

describe('Testing a new S3Client exception', () => {
  test('Creating a new S3Client instance should result in an error being thrown', () => {
    expect(() => {
      new SQSClient({});
    }).toThrow(new Error('constructor error'));
  });
});

Answer 2

If you're wondering how to achieve this using vitest, I'm not entirely sure. However, if you switch to jest, you might be able to implement something similar:

jest.mock('@aws-sdk/client-s3', () => {
  return {
    S3Client: jest.fn().mockImplementation(() => {
      throw new Error('constructor error');
    }),
  };
});

describe('Testing a new S3Client exception', () => {
  test('Creating a new S3Client instance should result in an error being thrown', () => {
    expect(() => {
      new SQSClient({});
    }).toThrow(new Error('constructor error'));
  });
});

Create a simulated constructor to generate an error

Answer №1

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