test: add comprehensive bash test suite

- Implement tests/run_tests.sh with mocked environment
- Cover color conversion, multi-format output, and config loading
- Verify clipboard and notification integrations via mocks
- Document testing procedure in README.md

README.md

@@ -102,6 +102,18 @@ copy   = true   # copy result to clipboard
 notify = true   # show desktop notification with the copied value
 ```
 
+## 🧪 Testing
+
+The project includes a comprehensive test suite that verifies color conversion, configuration loading, and system integrations (clipboard/notifications) using mocks.
+
+To run the tests:
+
+```bash
+./tests/run_tests.sh
+```
+
+The test script creates a temporary isolated environment, so it won't affect your system configuration or active clipboard.
+
 ## 🤝 Credits
 
 The `wl-colorpicker-plasma` integration is based on the original work by [SASUPERNOVA](https://github.com/SASUPERNOVA/wl-colorpicker-plasma).