Fixed how_to_develop.md Unit Tests saying tox is required

docs/how_to_develop.md

@@ -14,17 +14,14 @@ If you're interested in taking one of these on, let me know and I will provide m
 
 ## Unit Tests
 
-To run all Unit Tests,
-install tox and Python 2.7 up to the latest python version supported (consult the file tox.ini).
-Then,
-run the command `tox` on the root of this project (where the main setup.py file is on).
-
-If you would like to only run the Unit Tests for Python version 2.7,
-you can run the command `tox -e py27`
+If you would like to run all Unit Tests,
+all you need is a supported Python Interpreter.
+You can consult the list of supported interpreter for unit testing on the `tox.ini` file.
+Then, just run the command `python -m tests`
 
 If you would like to run a single Unit Test,
 you do not need to use tox,
-you can directly run it with your current python interpreter.
+you can directly run it with your installed Python Interpreter.
 First you need to figure out what is the test full name.
 For example:
 ```python
@@ -37,3 +34,14 @@ Equivalent example/way, but unrecommended:
 ##          test_package.tests_module.test_class_name.test_function_name
 python -m unittest tests.test_parser.TestLalrStandard.test_lexer_error_recovering
 ```
+
+### tox
+
+To run all Unit Tests with tox,
+install tox and Python 2.7 up to the latest python interpreter supported (consult the file tox.ini).
+Then,
+run the command `tox` on the root of this project (where the main setup.py file is on).
+
+And, for example,
+if you would like to only run the Unit Tests for Python version 2.7,
+you can run the command `tox -e py27`