more CONTRIBUTING updates

Author: alexcjohnson

CONTRIBUTING.md

@@ -51,9 +51,7 @@ When a change in renderer code doesn't reflect in your browser as expected, this
 
 Writing Python 2/3 compatible code might be a challenging task for contributors used to working on one particular version, especially new learners who start directly with Python 3.
 
-From the #892, we started to adopt `python-future` instead of `six` as our tool to better achieve the goal where we can mainly write Python 3 code and make it back-compatible in Python 2.7 (last Python 2 version Dash supports before it gets deprecated).
-
-Please refer to [this list of idioms](https://python-future.org/compatible_idioms.html "https://python-future.org/compatible_idioms.html") for more details on working with `python-future`.
+We use `python-future` as our tool to  mainly write Python 3 code and make it back-compatible to Python 2.7 (the only Python 2 version Dash supports). Please refer to [this list of idioms](https://python-future.org/compatible_idioms.html "https://python-future.org/compatible_idioms.html") for more details on working with `python-future`.
 
 ## Git
 
@@ -101,13 +99,15 @@ Emojis make the commit messages :cherry_blossom:. If you have no idea about what
 
 ### Coding Style
 
-We use both `flake8` and `pylint` for basic linting check, please refer to the relevant steps in `.circleci/config.yml`.
-
-Note that we also start using [`black`](https://black.readthedocs.io/en/stable/) as formatter during the test code migration.
+We use `flake8`, `pylint`, and [`black`](https://black.readthedocs.io/en/stable/) for linting. please refer to the relevant steps in `.circleci/config.yml`.
 
 ## Tests
 
-We started migrating to [pytest](https://docs.pytest.org/en/latest/) from `unittest` as our test automation framework. You will see more testing enhancements in the near future. To run the tests, see the commands in the `package.json` (such as `npm run test.integration`)
+Our tests use Google Chrome via Selenium. You will need to install [ChromeDriver](http://chromedriver.chromium.org/getting-started) matching the version of Chrome installed on your system. Here are some helpful tips for [Mac](https://www.kenst.com/2015/03/installing-chromedriver-on-mac-osx/) and [Windows](http://jonathansoma.com/lede/foundations-2018/classes/selenium/selenium-windows-install/).
+
+We use [pytest](https://docs.pytest.org/en/latest/) as our test automation framework, plus [jest](https://jestjs.io/) for a few renderer unit tests. You can `npm run test` to run them all, but this command simply runs `pytest` with no arguments, then `cd dash-renderer && npm run test` for the renderer unit tests.
+
+Most of the time, however, you will want to just run a few relevant tests and let CI run the whole suite. `pytest` lets you specify a directory or file to run tests from (eg `pytest tests/unit`) or a part of the test case name using `-k` - for example `pytest -k cbcx004` will run a single test, or `pytest -k cbcx` will run that whole file. See the [testing tutorial](https://dash.plotly.com/testing) to learn about the test case ID convention we use.
 
 ### Unit Tests
 
@@ -119,8 +119,6 @@ Note: *You might find out that we have more integration tests than unit tests in
 
 We introduced the `dash.testing` feature in [Dash 1.0](https://community.plotly.com/t/announcing-dash-testing/24868). It makes writing a Dash integration test much easier. Please read the [tutorial](http://dash.plotly.com/testing) and add relevant integration tests with any new features or bug fixes.
 
-To run the integration tests, you may have to [install circleci](https://circleci.com/docs/2.0/local-cli/).
-
 ## Financial Contributions
 
 Dash, and many of Plotly's open source products, have been funded through direct sponsorship by companies. [Get in touch] about funding feature additions, consulting, or custom app development.