docs: add ci docs.

Add initial CI docs.

Signed-off-by: Giacomo Dematteis <giacomo.dematteis@nordicsemi.no>

Author: DematteisGiacomo

docs/common/test_and_ci_setup.md

@@ -1,7 +1,98 @@
-# Test and CI Setup
+# Testing and CI Setup
 
-## On-commit tests - fast
-- Explanation of on-commit tests.
+The Asset Tracker Template features a comprehensive testing infrastructure with tests run both on real hardware (on target) and emulation.
+Code analysis is performed through compliance checks and SonarCloud analysis.
 
-## Nightly - speed not that important, run on target
-- Explanation of nightly tests.
+## CI Pipeline Structure
+
+The CI pipeline is composed by the following workflows:
+- .github/workflows/build.yml: for building the devices firmware.
+- .github/workflows/target-test.yml: for running tests on real hardware.
+- .github/workflows/build-target-test.yml: workflow that glues together build.yml and target-test.yml.
+- .github/workflows/sonarcloud.yml: for building and running tests on emulation, and run Sonarcloud analysis.
+- .github/workflows/compliance.yml: for static compliance checks.
+
+Additionally we are using AI assistant in .github/workflows/ai-review.yaml. It's an AI reviewer that runs on pull request.
+Developer can choose to run it or not with a label.
+
+
+The CI pipeline is triggered as follows:
+- On pull request: build.yml, sonarcloud.yml, compliance.yml
+The goal initially was to have a CI faster than ~5 minuts on PR. Current CI takes ~4minuts, with sonarcloud being bottleneck.
+No target tests are run on PR to avoid instabilities.
+
+- Direct pushes to the main branch when merge: build-target-test.yml, sonarcloud.yml
+Only "fast" targets tests are run. Avoiding excessively time-consuming tests.
+
+- Nightly schedule: build-target-test.yml
+Full set of target tests. Includes "slow" tests such as full-modem-fw fota test and power consumption test.
+
+### Testing
+
+#### Hardware Testing
+The project includes tests that run on real hardware devices, implemented in the `.github/workflows/target-test.yml` workflow. Key features include:
+
+Tests on target are performed on self-hosted runners.
+Read more here and how to set up your own instance for your project: https://docs.github.com/en/actions/hosting-your-own-runners/managing-self-hosted-runners/about-self-hosted-runners
+
+
+- Tests run on multiple target devices:
+  - nRF9151 DK
+  - Thingy:91 X
+- Uses self-hosted runners labeled according to the connected device
+- Runs in a containerized environment with hardware access
+- pytest as test runner
+- Supports Memfault integration for symbol file uploads
+- Generates detailed test reports and logs
+- Flexible test execution with support for specific test markers and paths
+
+Try out tests locally: tests/on_target/README.md
+
+#### Emulation Testing
+Emulation tests are implemented as part of the SonarCloud workflow (`.github/workflows/sonarcloud.yml`). These tests:
+
+- Run on the native_sim platform using Twister
+- Execute integration tests in an emulated environment
+- Generate code coverage reports
+- Use build wrapper for accurate code analysis
+
+### Code Analysis
+
+#### SonarCloud Analysis
+The SonarCloud integration (`.github/workflows/sonarcloud.yml`) provides:
+
+- Static code analysis for C/C++ files
+- Code coverage reporting
+- Pull request analysis and main branch analysis
+- Continuous monitoring of code quality metrics
+- Separate analysis configurations for main branch and pull requests
+
+#### Compliance Testing
+Compliance checks are implemented in `.github/workflows/compliance.yml` and include:
+
+- Codeowners validation
+- Devicetree compliance
+- Git commit message linting
+- Identity checks
+- Code style and formatting (Nits)
+- Python code linting
+- Kernel coding style checks (checkpatch)
+
+
+### Key Features
+
+1. **Modularity**: Each aspect of testing is handled by a dedicated workflow
+2. **Comprehensive Coverage**: Combines hardware testing, emulation, and static analysis
+3. **Detailed Reporting**: Generates test reports, coverage data, and compliance checks
+4. **Flexibility**: Supports different test configurations and target devices
+5. **Quality Assurance**: Multiple layers of validation ensure code quality
+
+## Test Results and Artifacts
+
+Each workflow generates specific artifacts:
+- Hardware test results and logs
+- Coverage reports
+- Compliance check outputs
+- SonarCloud analysis reports
+
+Artifacts are available in the GitHub Actions interface and can be used for debugging and quality assurance purposes.