Unit testing ValidationError

Next, let's focus on testing the ValidationError class. Once again, we will move the validation.js file into its own director:

$ cd src/validators/errors/ && \
  mkdir validation-error && \
  mv validation-error.js validation-error/index.js && \
  cd ../../../

Now, create a new file atsrc/validators/errors/validation-error/index.unit.test.js to house our unit tests:

import assert from 'assert';
import ValidationError from '.';

describe('ValidationError', function () {
  it('should be a subclass of Error', function () {
    const validationError = new ValidationError();
    assert.equal(validationError instanceof Error, true);
  });
  describe('constructor', function () {
    it('should make the constructor parameter accessible via the `message` property of the instance', function () {
      const TEST_ERROR = 'TEST_ERROR';
      const validationError = new ValidationError(TEST_ERROR);
      assert.equal(validationError.message, TEST_ERROR...