code: function oneOf (list, msg) {
      if (msg) flag(this, 'message', msg);
      var expected = flag(this, 'object')
        , flagMsg = flag(this, 'message')
        , ssfi = flag(this, 'ssfi');
      new Assertion(list, flagMsg, ssfi, true).to.be.an('array');
  
      this.assert(
          list.indexOf(expected) > -1
        , 'expected #{this} to be one of #{exp}'
        , 'expected #{this} to not be one of #{exp}'
        , list
        , expected
      );
    }
docs: ### .oneOf(list[, msg])
  
  Asserts that the target is a member of the given array `list`. However,
  it's often best to assert that the target is equal to its expected value.
  
  expect(1).to.equal(1); // Recommended
  expect(1).to.be.oneOf([1, 2, 3]); // Not recommended
  
  Comparisons are performed using strict (`===`) equality.
  
  Add `.not` earlier in the chain to negate `.oneOf`.
  
  expect(1).to.equal(1); // Recommended
  expect(1).to.not.be.oneOf([2, 3, 4]); // Not recommended
  
  `.oneOf` accepts an optional `msg` argument which is a custom error message
  to show when the assertion fails. The message can also be given as the
  second argument to `expect`.
  
  expect(1).to.be.oneOf([2, 3, 4], 'nooo why fail??');
  expect(1, 'nooo why fail??').to.be.oneOf([2, 3, 4]);
  
  @name oneOf
  @param {Array<*>} list
  @param {String} msg _optional_
  @namespace BDD
  @api public