docs: clarify supported Python testing frameworks

Docs-only update to clarify which Python testing frameworks are supported
by the extension and how unsupported frameworks (e.g. behave) currently behave.

This helps set expectations for users and provides additional context
for feature requests such as #25330.

Author: DakotaB75

README.md

@@ -99,7 +99,32 @@ Learn more about the rich features of the Python extension:
 -   [Environments](https://code.visualstudio.com/docs/python/environments): Automatically activate and switch between virtualenv, venv, pipenv, conda and pyenv environments.
 -   [Refactoring](https://code.visualstudio.com/docs/python/editing#_refactoring): Restructure your Python code with variable extraction and method extraction. Additionally, there is componentized support to enable additional refactoring, such as import sorting, through extensions including [isort](https://marketplace.visualstudio.com/items?itemName=ms-python.isort) and [Ruff](https://marketplace.visualstudio.com/items?itemName=charliermarsh.ruff).
 
+### Testing framework support
 
+The Python extension provides built-in integration with the VS Code Test Explorer
+for the following Python testing frameworks:
+
+- `unittest`
+- `pytest`
+
+These frameworks are directly supported through dedicated test discovery,
+execution, and result reporting implementations.
+
+#### Other testing frameworks (e.g. behave)
+
+Additional testing frameworks such as `behave` (BDD / Gherkin-style testing)
+are not currently supported out of the box.
+
+While these frameworks can still be executed manually via the terminal,
+they do not integrate with the VS Code Test Explorer at this time.
+
+Supporting additional frameworks would require:
+- Implementing test discovery logic
+- Mapping results to the VS Code Testing API
+- Long-term maintenance and ownership
+
+Community feedback helps prioritize which additional testing frameworks
+may be considered for future support.
 
 ## Supported locales