feat: add lint and unit test workflow checks for pull requests

[bryantbiggs]

Description

• add lint, type check, and unit test checks to CI workflow
  • test snapshots are added to aid in visually inspecting what has changed since we are converting some JSON payload into another JSON type payload that will be sent to Slack
• replace Python map of mixed message payloads with discrete JSON payloads separated by file and by type. JSON event payloads that are in the SNS message format are stored under functions/messages/, and JSON raw event message payloads are stored under functions/events/*. SNS messages are what are currently trigger the lambda handler, but by having the raw events as well we can make developing and testing custom messages for new event types easier; in the end they are just stringified JSON payloads store din the Message attribute of the SNS message that triggers the function
• the slack-notify-simple example has been updated to produce an environment variables file to aid in local integrations testing
• an integration testing file integration_test.py has been added to test the resources live (using the SNS topic and Lambda handler created by the slack-notify-simple example project)
• documentation has been updated to explain and demonstrate how to work with the Python codebase and tests locally

Motivation and Context

• Improve testing facilities to aid in pull request reviews; next step is to start adding more event types supported

Breaking Changes

• No

How Has This Been Tested?

• I have tested and validated these changes using one or more of the provided examples/* projects
  • Unit tests => see GitHub action workflow results or run pipenv run test
  • Integration test => deployed slack-notify-simple project using my provided webhook URL and then ran pipenv run python integration_test.py

[bryantbiggs]

and it fails, fantastic 🎉! time to fix

[bryantbiggs]

this threw me for a loop. some events are shown in the SNS event format thats delivered to the lambda when invoked, and others are in the raw message format (that would in theory be passed to something like aws sns publish --topic-arn "xxx" --message "<message>").

Its this 2nd format, the raw format, that had me scratching my head as to why this https://github.com/terraform-aws-modules/terraform-aws-notify-slack/blob/master/functions/notify_slack.py#L153 wasn't failing because they don't have an enclosing SNS event format with Records: []. But the current tests don't test through the actual lambda handler, they short-circuit through this function https://github.com/terraform-aws-modules/terraform-aws-notify-slack/blob/master/functions/notify_slack.py#L101

[antonbabenko]

This PR is included in version 4.22.0 🎉

[antonbabenko]

Very nice! Glad to see some more improvements in this rather popular module. Thanks @bryantbiggs !

[github-actions]

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