[travis-ci] Trigger a Travis-CI rebuild without pushing a commit?

If you have new project on GitHub which has .travis.yml, but was never tested, you can run tests without commit this way:

  1. enable testing in Travis CI setings
  2. open project page on GitHub
  3. open settings -> webhooks and services
  4. find Travis CI in services and press edit button
  5. press "Test service"