[BEAM-13894] Unit test utilities in the ptest package

[jrmccluskey]

Updates the ptest package to unit test the utility transforms provided.

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ValidatesRunner compliance status (on master branch)

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---					---
Java
Python	---					---
XLang						---

Examples testing status on various runners

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---	---	---	---	---	---	---
Java	---		---	---	---	---	---
Python	---	---	---	---	---	---	---
XLang	---	---	---	---	---	---	---

Post-Commit SDK/Transform Integration Tests Status (on master branch)

Go	Java	Python

Pre-Commit Tests Status (on master branch)

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

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

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI.

[codecov]

Codecov Report

Merging #16830 (d1d0524) into master (7975127) will decrease coverage by 27.76%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master   #16830       +/-   ##
===========================================
- Coverage   74.65%   46.89%   -27.77%     
===========================================
  Files         655      204      -451     
  Lines       82347    20122    -62225     
===========================================
- Hits        61477     9436    -52041     
+ Misses      19870     9686    -10184     
  Partials     1000     1000               

Impacted Files	Coverage Δ
sdks/go/pkg/beam/testing/ptest/ptest.go	48.97% <ø> (ø)
sdks/python/apache_beam/io/fileio.py
...amples/snippets/transforms/elementwise/tostring.py
...hon/apache_beam/portability/api/beam_fn_api_pb2.py
...n/apache_beam/examples/cookbook/bigquery_schema.py
...eam/runners/interactive/caching/streaming_cache.py
.../python/apache_beam/io/gcp/datastore/v1new/util.py
sdks/python/apache_beam/io/aws/s3filesystem.py
...cp/internal/clients/storage/storage_v1_messages.py
.../python/apache_beam/io/gcp/bigquery_io_metadata.py
... and 444 more

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[jrmccluskey]

R: @lostluck @damccorm

[damccorm]

Left one small style comment, but otherwise LGTM!

[damccorm]

Style nit (treat any style comments from me with a grain of salt since I'm new to the language): prefer identifying the function in your error - https://github.com/golang/go/wiki/TestComments#identify-the-function - and probably use "got, want" style, so ("Run(p) = %q, want nil", err)

In particular here (and below) the pipeline creation isn't really what's failing, its running the pipeline which could be an issue with Create, Run, or passert.EqualsList (but hopefully not since that's not what we're testing)

[jrmccluskey]

Linking to golang documentation is always appreciated. I've updated the message to your format with the one tweak of specifying that we returned an error. Thank you!

[lostluck]

LGTM Thanks! Sorry for the delay.