# Testing and launching an experiment

#### Contents

- Further reading

Once you've written your code, it's a good idea to test that each variant behaves as you'd expect. If you find out your implementation had a bug after you've launched the experiment, you lose days of effort as the experiment results can no longer be trusted.

The best way to do this is **adding an optional override** to your [release conditions](/content/docs/feature-flags/creating-feature-flags#release-conditions/index.html). For example, you can create an override to assign a user to the `test` variant if their email is your own (or someone in your team). To do this:

1. Go to your experiment feature flag.
2. Ensure the feature flag is enabled by checking the "Enable feature flag" box.
3. Add a new condition set with the condition to `email = your_email@domain.com`. Set the rollout percentage for this set to 100%.
   - In cases where `email` is not available (such as when your users are logged out), you can use a parameter like `utm_source` and append `?utm_source=your_variant_name` to your URL.
4. Set the optional override for the variant you'd like to assign these users to.
5. Click "Save".

Once you test it works, launch your experiment.