When creating a new branch, we copied all WAL from the source timeline
to the new one, and it was being picked up and digested into the
repository on first use of the timeline. Fix by copying the WAL only
up to the branch's starting point.
We should probably move the branch-creation code from the CLI to page
server itself - that's what I was starting to hack on when I noticed this
bug - but let's fix this first.
Add a regression test. To test multiple branches, enhance the python
test fixture to manage multiple running Postgres instances. Also, for
convenience, add a function to the postgres fixture to open a connection
to the server with psycopg2.
Somehow I never learned this part correctly: relative imports use the
syntax "import .file" for a file sitting in the same directory.
This error wasn't terribly obvious, but the Pylance linter is yelling at
me so I'll fix it now before anyone else notices.
Use pytest to manage background services, paths, and environment
variables.
Benefits:
- Tests are a little easier to write.
- Cleanup is more reliable. You can CTRL-C a test and it will still shut
down gracefully. If you manually start a conflicting process, the test
fixtures will detect this and abort at startup.
- Don't need to worry about remembering '--test-threads=1'
- Output of sub-processes can be captured to files.
- Test fixtures configure everything to operate under a single test
output directory, making it easier to capture logs in CI.
- Detects all the necessary paths if run from the git root, but can also
run from arbitrary paths by setting environment variables.
There is also a deliberately broken test (test_broken.py) that can be
used to test whether the test fixtures properly clean up after
themselves. It won't run by default; the comment at the top explains how
to enable it.
