I will answer this question myself, as it is now clear.
Basically, if you follow the instructions and configure Pull Request Builder, this is cron.
For each periodic run, he discovers that after the last check, a new commit is discovered, or "test it please." If so, it will invoke the assembly.
Note that PRB will create a temp branch that merges your PR code into the default branch. And it will warn you if there is a conflict in the code.
Hope this helps.
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