fixes dbc.RadioButton bug

CONTRIBUTING.md

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+# Contributing
+
+## Runnning tests offline
+
+When submitting a PR github can run the full testsuite using github actions. For running the tests offline you
+need to make sure you have installed all the required offline testing requirements:
+
+### virtual environment
+
+First create a new virtual environment:
+
+`$ python -m venv venv`
+`$ source venv/bin/activate`
+
+### install dependencies and CLI tools
+
+First make sure you have the latest version of pip itself: 
+`$ python -m pip install -U pip setuptools wheel`
+
+Then install the whole package including dependencies:
+`$ pip install -e .`
+
+(this also install the CLI tools in the path)
+
+### install testing dependencies
+
+There are additional libraries such as selenium, xgboost, catboost, lightgbm etc needed for testing:
+
+`$ pip install -r requirements_testing.txt`
+
+(lightgbm may give some headaches when installing with pip, so can also `brew install lightgbm` instead)
+
+### install chromedriver for integration tests
+
+For the integration tests we use Selenium which launches a headless version of google chrome to launch a dashboard
+in the browser and then checks that there are no error messages. In order to run these tests you need to download
+a chromedriver that is compatible with your current installation of chrome at https://chromedriver.chromium.org/
+
+You then unzip it and copy it to `$ cp chromedriver /usr/local/bin/chromedriver`
+and on OSX allow it to be run with `$ xattr -d com.apple.quarantine /usr/local/bin/chromedriver`.
+
+### running the tests
+
+The tests should now run in the base directory with
+
+`$ pytest .`