There are no automated tools for testing.

From what I learned over the years, this is the life cycle of a major change:

1. Write the code and deploy on the development site https://dev.stackoverflow.com
2. Basic testing by the developers and probably more team members.
3. Deploy the change here, on MSE.
4. Collect bug reports, feature requests, and feedback about the new feature.
5. Fix bugs while it's deployed on MSE, improve, change, etc.
6. Deploy network wide, if there are no red lights blinking.
7. Happy dance. (possibly while wearing unicorn masks)

Good example is the recent major change: Let’s improve our site navigation

There are no automated tools for testing.

From what I learned over the years, this is the life cycle of a major change:

1. Write the code and deploy on the development site https://dev.stackoverflow.com
2. Basic testing by the developers and probably more team members.
3. Deploy the change here, on MSE.
4. Collect bug reports, feature requests, and feedback about the new feature.
5. Fix bugs while it's deployed on MSE, improve, change, etc.
6. Deploy network wide, if there are no red lights blinking.
7. Happy dance. (possibly while wearing unicorn masks)

Good example is the recent major change: Let’s improve our site navigation