All pull requests and merges are tested in Travis CI based on the .travis.yml file.
Usually, a link to your specific travis build appears in pull requests, but if not, you can find it on the pull requests page
The only way to trigger Travis CI to run again for a pull request, is to submit another change to the pull branch.
You will need Tox installed to run the tests against the supported Python versions.
$ pip install tox
$ tox