Running bundle exec rake autospec runs all the tests that are in this folder: discourse/spec at main · discourse/discourse · GitHub
Yes, but depending on your computer’s speed it could take a while. It takes me about 10 minutes to run the tests. Green dots indicate passing tests, so they are always nice to see.
Depending on why you are installing Discourse locally, you might not need to run the test suite. You’ll need to be able to run it if ever send any pull requests to Discourse.