text: if (!chai) {
    var chai = require('..');
  }
  
  suite('plugins', function () {
  
    function plugin (chai) {
      if (chai.Assertion.prototype.testing) return;
  
      Object.defineProperty(chai.Assertion.prototype, 'testing', {
        get: function () {
          return 'successful';
        }
      });
    }
  
    test('basic usage', function () {
      chai.use(plugin);
      var expect = chai.expect;
      expect(expect('').testing).to.equal('successful');
    });
  
    test('double plugin', function () {
      chai.expect(function () {
        chai.use(plugin);
      }).to.not.throw();
    });
  });
  