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describe('plugins', function () {
  function plugin (chai) {    if (chai.Assertion.prototype.testing) return;
    Object.defineProperty(chai.Assertion.prototype, 'testing', {      get: function () {        return 'successful';      }    });  }
  it('basic usage', function () {    chai.use(plugin);    var expect = chai.expect;    expect(expect('').testing).to.equal('successful');  });
  it('double plugin', function () {    chai.expect(function () {      chai.use(plugin);    }).to.not.throw();  });
  it('.use detached from chai object', function () {    function anotherPlugin (chai) {      Object.defineProperty(chai.Assertion.prototype, 'moreTesting', {        get: function () {          return 'more success';        }      });    }
    var use = chai.use;    use(anotherPlugin);
    var expect = chai.expect;    expect(expect('').moreTesting).to.equal('more success');  });});