Testing ADR (#9562)

* Update contributing with new links
* Testing ADR

Signed-off-by: Derek Nola <derek.nola@suse.com>

CONTRIBUTING.md

@@ -2,9 +2,9 @@
 
 Thanks for taking the time to contribute to K3s!
 
-Please review and follow the [Code of Conduct](https://github.com/k3s-io/k3s/blob/master/CODE_OF_CONDUCT.md).
+Please review and follow the [Code of Conduct](CODE_OF_CONDUCT.md).
 
-Contributing is not limited to writing code and submitting a PR. Feel free to submit an [issue](https://github.com/k3s-io/k3s/issues/new/choose) or comment on an existing one to report a bug, provide feedback, or suggest a new feature. You can also join the discussion on [slack](https://slack.rancher.io/).
+Contributing is not limited to writing code and submitting a PR. Feel free to submit an [issue](https://github.com/k3s-io/k3s/issues/new/choose) or comment on an existing one to report a bug, provide feedback, or suggest a new feature. You can also join the discussion on [slack](https://rancher-users.slack.com/channels/k3s).
 
 Of course, contributing code is more than welcome! To keep things simple, if you're fixing a small issue, you can simply submit a PR and we will pick it up. However, if you're planning to submit a bigger PR to implement a new feature or fix a relatively complex bug, please open an issue that explains the change and the motivation for it. If you're addressing a bug, please explain how to reproduce it.
 
@@ -12,7 +12,11 @@ If you're interested in contributing documentation, please note the following:
 - Doc issues are raised in this repository, and they are tracked under the `kind/documentation` label.
 - Pull requests are submitted to the K3s documentation source in the [k3s-io docs repository.](https://github.com/k3s-io/docs).
 
-If you're interested in contributing new tests, please see the `TESTING.md` in the tests directory.
+If you're interested in contributing new tests, please see the [TESTING.md](./tests/TESTING.md).
+
+## Code Convetion
+
+See the [code convetions documentation](./docs/contrib/code_conventions.md) for more information on how to write code for K3s.
 
 ### Opening PRs and organizing commits
 PRs should generally address only 1 issue at a time. If you need to fix two bugs, open two separate PRs. This will keep the scope of your pull requests smaller and allow them to be reviewed and merged more quickly.

docs/adrs/testing-2024.md

@@ -0,0 +1,62 @@
+# Testing in K3s
+
+Date: 2024-02-23
+
+# Context
+
+## Background
+
+Currently, Testing in K3s is categorized into various types and spread across Github Actions and Drone CI. The types are as follows:
+
+GitHub Actions:
+- Unit Tests: For testing individual components and functions, following a "white box" approach.
+- Integration Tests: Test functionalities across multiple packages, using "black box" testing.
+- Smoke Tests: Simple tests to ensure basic functionality works as expected. Broken into:
+    - Cgroup: Tests cgroupv2 support.
+    - Snapshotter: tests btrfs and overlayfs snapshotter support.
+    - Install tests: Tests the installation of K3s on various OSes.
+
+Drone CI:
+- Docker Tests: Run clusters in containers to test basic functionality. Broken into:
+    - Basic Tests: Run clusters in containers to test basic functionality.
+    - Sonobuoy Conformance Tests: Run clusters in containers to validate K8s conformance. Runs on multiple database backends.
+- End-to-End (E2E) Tests: Cover multi-node configuration/administration.
+
+- Performance Tests: Use Terraform to test large-scale deployments of K3s clusters. These were legacy tests and are never run in CI.
+
+## Problems
+
+- The current testing infrastructure is complex and fragmented, leading to maintenance overhead. Not all testing is grouped inside the [tests directory](../../tests/).
+- GitHub Actions had limited resources, making it unsuitable for running larger tests.
+- GitHub Actions only supported hardware virtualiztion on Mac runners and that support was often broken.
+- Drone CI cannot handle individual testing failures. If a single test fails, the entire build is marked as failed.
+
+## New Developments
+
+As of late January 2024, GitHub Actions has made significant improvements:
+- The resources available to open source GitHub Actions have been doubled, with 4 CPU cores and 16GB of RAM. See blog post [here](https://github.blog/2024-01-17-github-hosted-runners-double-the-power-for-open-source/).
+- Standard (i.e. free) Linux runners now support Nested Virtualization
+
+## Decision
+
+We will move towards a single testing platform, GitHub Actions, and leverage the recent improvements in resources and nested virtualization support. This will involve the following changes:
+
+- Test distribution based on size and complexity:
+    - Unit, Integration: Will continue to run in GitHub Actions due to their smaller scale and faster execution times.
+    - Install Test, Docker Basic, and E2E Tests: Will run in GitHub Actions on standard linux runners thanks to recent enhancements.
+    - Docker Conformance and large E2E Tests (2+ nodes): Still utilize Drone CI for resource-intensive scenarios.
+
+- Consolidating all testing-related files within the "tests" directory for better organization and clarity.
+- Cgroup smoke tests will be removed. As multiple Operating Systems now support CgroupV2 by default, these tests are no longer relevant.
+- Snapshotter smoke test will be converted into a full E2E test.
+- Remove of old performance tests, as they are no longer relevant. Scale testing is already handled by QA as needed. 
+
+Tracking these changes is with [this issue](https://github.com/k3s-io/k3s/issues/9477)
+
+## Consequences
+
+- The testing infrastructure will be more organized and easier to maintain.
+- The move to GitHub Actions will allow for faster feedback on PRs and issues.
+- The removal of old tests will reduce the maintenance overhead.
+- New testing process can be used as a model for related projects.
+