At this point, I can run tests via Jenkins on scratch builds but only for branched content. It would be good to have an option to run tests for custom SRPMs as well. General workflow that I usually use when pushing updated to Fedora is as follows:
1. Change sources/specfile/patches etc. in one branch
2. Issue 'fedpkg scratch-build --srpm --target fXX' to test the changes in the build environment in branches where I want to push the change
3. Wait for test results from CI

This could work with tmt in Jenkins as well but there is a problem, that I cannot test scratch builds that are initiated with --srpm. Only content that is pushed to branch is tested. I know that tests are run for PRs but as we discussed with @mvadkert on IRC, it is not reasonable to expect every maintainer to push changes to dist-git for his/her own component via PRs.

@msrb mentioned that there is one caveat and that is how to choose which tests to run. Each scratch is for a specific target like f34 for instance. Tests taken from that branch - either tests that are directly in the dist-git repo, or tests that are listed in .fmf file in dist-git in that branch could be run for the build.