LIN-579 Provide user with pipeline test skeleton

[yoonspark]

Summary

As a first story of the Enable Pipeline Testing epic, this PR implements a bare minimal scaffolding for pipeline testing, where:

• Each function in the module gets a corresponding test case
• Each test case simply calls the tested function within a try-catch block
• Comments are provided to instruct the user to adjust test logic as needed

Though very simple, this bare minimal templating may still deliver some value to the user as it provides them a starting point for pipeline testing (better to have something than nothing). Again, this is a first story for the epic, and the plan is to improve on it with subsequent stories.

Changes

• Add a new Jinja template for rudimentary scaffolding of pipeline testing
• Add a new (hidden) method to BasePipelineWriter to fill in the Jinja template
• Add new unit tests for the pipeline test scaffolding

Testing

Unit tests were added to cover the new functionality.

Ticket(s)

• LIN-579

[lionsardesai]

looks good. comments made are not show stoppers. can also be done in subsequent stories.