[BEAM-8575] Add a Python test to test windowing in DoFn finish_bundle()

[liumomo315]

This test is the Python parity for the Java ParDo test testWindowingInStartAndFinishBundle.

---

Thank you for your contribution! Follow this checklist to help us incorporate your contribution quickly and easily:

• Choose reviewer(s) and mention them in a comment (R: @username).
• Format the pull request title like [BEAM-XXX] Fixes bug in ApproximateQuantiles, where you replace BEAM-XXX with the appropriate JIRA issue, if applicable. This will automatically link the pull request to the issue.
• If this contribution is large, please file an Apache Individual Contributor License Agreement.

See the Contributor Guide for more tips on how to make review process smoother.

Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---		---	---
Java
Python		---			---	---
XLang	---	---	---		---	---	---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website
Non-portable
Portable	---		---	---

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

[liumomo315]

R: @y1chi

PTAL Yichi! Thanks:)

[y1chi]

LGTM, I wonder would it be better to move the timestamp assignment to beam.Create() and combine the map function into the MyDoFn.

[liumomo315]

Thanks for the quick review!

move the timestamp assignment to beam.Create()

This can be done, but does not make much difference, since we still want both the process() and finish_bundle() to do something in this test, and see the reason below.

and combine the map function into the ParDo.

I think it's clearer to separate the Map from the test DoFn. The purpose of this test is to verify that after a DoFn with finish_bundle() implemented, it will produce results both from process() and finish_bundle(). More specifically, it wants to make sure that when windowing is involved, the output will be correct after the DoFn. The last Map is simply to print out all outputs from the test DoFn. Thoughts?

[y1chi]

@tvalentyn could you help to merge?

[liumomo315]

Thanks Yichi for the review:)

[tvalentyn]

Thanks, @liumomo315 and @y1chi ! Somehow I missed the last comment, merged now!

[tvalentyn]

@liumomo315 Please run ValidatesRunner tests when marking new tests as "VR". The command to trigger the tests can be found in .test-infra/jenkins/README file, the link is available in the PR template. To run those tests you can just comment on the PR: Run Dataflow Python ValidatesRunner

[liumomo315]

Thanks for the hints, Valentyn! Will do that for my new PRs.