Better Testing Coming to Google AdWords

Improving your campaigns in AdWords is the goal of optimization. Now AdWords allows for easier ways to test changes to your campaign with drafts and experimenting features.

Drafts are where you setup your changes and when ready you turn them on as experiments.

You can then run your original campaign with a controlled experiment and easily apply your experiment to your campaign if the test is successful.

Source: Inside AdWords: Test with confidence using campaign drafts and experiments