developer guide enhancements.

CONTRIBUTING.md

@@ -34,28 +34,84 @@ the document that explains the way `sanic` manages dependencies inside the `setu
 | extras_require['dev']                     | Additional Development requirements to add contributing                    | pip3 install -e '.[dev]'     |
 | extras_require['docs']                    | Dependencies required to enable building and enhancing sanic documentation | pip3 install -e '.[docs]'    |
 
-## Running tests
+## Running all tests 
-
+To run the tests for Sanic it is recommended to use tox like so:
-To run the tests for sanic it is recommended to use tox like so:
 
 ```bash
 tox
 ```
-
 See it's that simple!
 
+`tox.ini` contains different environments. Running `tox` without any arguments will 
+run all unittests, perform lint and other checks. 
+
+## Run unittests : 
+`tox` environment -> `[testenv]`
+
+To execute only unittests, run `tox` with environment like so: 
+
+```bash
+tox -e py36 -v -- tests/test_config.py
+# or 
+tox -e py37 -v -- tests/test_config.py
+```
+
+## Run lint checks : 
+`tox` environment -> `[testenv:lint]`
+
+Permform `flake8`, `black` and `isort` checks.
+```bash
+tox -e lint
+```
+
+## Run other checks : 
+`tox` environment -> `[testenv:check]`
+
+Perform other checks.
+```bash
+tox -e check
+```
+
+# Code Style 
+To maintain the code consistency, Sanic uses following tools. 
+
+1. [isort](https://github.com/timothycrosley/isort)
+2. [black](https://github.com/python/black)
+2. [flake8](https://github.com/PyCQA/flake8)
+
+
+## isort
+`isort` sorts Python imports. It divides imports into three 
+categories sorted each in alphabetical order. 
+  1. built-in
+  2. third-party
+  3. project-specific
+
+## black
+`black` is a Python code formatter.
+
+## flake8
+`flake8` is a Python style guide that wraps following tools into one.
+1. PyFlakes
+2. pycodestyle
+3. Ned Batchelder's McCabe script 
+
+`isort`, `black` and `flake8` checks are performed during `tox` lint checks. 
+
+Refer [tox](https://tox.readthedocs.io/en/latest/index.html) documentation for more details.
+
 ## Pull requests!
 
 So the pull request approval rules are pretty simple:
 1. All pull requests must pass unit tests.
 2. All pull requests must be reviewed and approved by at least
-one current collaborator on the project.
+  one current collaborator on the project.
 3. All pull requests must pass flake8 checks.
 4. All pull requests must be consistent with the existing code.
 5. If you decide to remove/change anything from any common interface
-a deprecation message should accompany it.
+  a deprecation message should accompany it.
 6. If you implement a new feature you should have at least one unit
-test to accompany it.
+  test to accompany it.
 7. An example must be one of the following:
   * Example of how to use Sanic
   * Example of how to use Sanic extensions