[BEAM-8148] Allow arguments to be passed to python tests from tox cli

[chadrik]

I don't know how to specify individual tests using gradle, and as a python developer, it's way too opaque for me to figure out on my own.

The developer wiki suggest calling the tests directly:

python setup.py nosetests --tests <module>:<test class>.<test method>

But this defeats the purpose of using tox, which is there to help users manage the myriad virtual envs required to run the different tests. Luckily, there is an easier way.

With this PR you can now do:

tox -e py27 -- --tests apache_beam.testing.synthetic_pipeline_test

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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.

[chadrik]

R: @robertwb
R: @mxm
R: @aaltay

[robertwb]

Thanks, this will be useful.

[chadrik]

Yep, someone with committer credentials should update the wiki once this goes in.

[chadrik]

Thanks @robertwb

Here's the link to the wiki article I was referring to https://cwiki.apache.org/confluence/display/BEAM/Python+Tips

[mxm]

Awesome, thanks!

[aaltay]

I updated https://cwiki.apache.org/confluence/display/BEAM/Python+Tips

Thank you!