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regexp.spec.js

import {strict as assert} from 'assert';

describe('Ways to create regexps (objects, literal, ...), (how) do they differ?', () => {
  it('a regexp is of type object', async () => {
    const regexp = /./;
    assert.equal(typeof regexp, 'object');
  });
  it('a regexp is an instance of RegExp', () => {
    const regexp = /./;
    assert(regexp instanceof RegExp);
  });
  it('a constructed regexp returns the same result as the literal', () => {
    const regexpLiteral = /abc/;
    const regexpConstruct = new RegExp('abc');
    assert.deepEqual(regexpLiteral.exec('abc'), regexpConstruct.exec('abc'));
  });
});

describe('RegExp groups', () => {
  it('a group does not effect the matched pattern', () => {
    const regexp = /(ab)c/; // the (...) is the group
    const result = regexp.exec('abcd');
    assert.deepEqual(result[0], 'abc');
  });
  it('a very simple group shows up in our match result, on index 1 (first group)', () => {
    const regexp = /(ab)c/;
    const result = regexp.exec('abcd');
    assert.equal(result[1], 'ab');
  });
  it('three groups are returned in index 1,2 and 3 of the match result', () => {
    const regexp = /(a)(b)(c)/;
    const result = regexp.exec('abcd');
    assert.equal(result[1], 'a');
    assert.equal(result[2], 'b');
    assert.equal(result[3], 'c');
  });
  it('using a group we can split a SIMPLE email', () => {
    const regexp = /(.+)@(.+)/;
    const result = regexp.exec('user@name.com');
    assert.deepEqual(Array.from(result), ['user@name.com', 'user', 'name.com']);
    assert.equal(result[0], 'user@name.com');
    assert.equal(result[1], 'user');
    assert.equal(result[2], 'name.com');
  });
  it('a named group is in the `groups` property of the match result', () => {
    const regexp = /(?<name>ab)/;
    const result = regexp.exec('abc');
    assert.equal(result.groups.name, 'ab');
  });
});

describe('What methods are on a regexp?', () => {
  it('a regexp can match itself', () => {
    const regexp = /abc/;
    const result = regexp.exec(regexp);
    assert.deepEqual(result[0], 'abc');
  });
});