Adding unit testing section

doc/source/contribution_and_api/index.rst

@@ -137,3 +137,4 @@ MAPDL commands mapped to PyMAPDL, see :ref:`ref_mapdl_commands`.
    post
    solution
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+   unit_testing

doc/source/contribution_and_api/unit_testing.rst

@@ -0,0 +1,42 @@
+.. _ref_unit_testing_contributing:
+
+Unit Testing
+===============
+
+Unit testing is highly important. It enables to check that the
+changes on the code are efficient and don't have an impact on
+other parts of the code. 
+
+Unit tests are in the ``tests`` directory inside this repository.
+
+Test Validation GitHub workflow
+-------------------------------
+
+`Codecov <https://github.com/codecov>`_ generates a coverage report of
+the committed code. It details how merging the Pull Request will impact the
+coverage. It is one of the checks that must be approved to
+merge the code.
+
+Creating a unit test 
+--------------------
+
+In the pymapdl repository, the tests are done with the **pytest package**. 
+
+To create a pytest file, its name must be one of the following forms:
+``filename_test.py`` or ``test_filename.py``.
+
+To create tests, please take note of the `pytest documentation <https://docs.pytest.org/en/7.2.x/>`_ .
+
+The `unit test <https://github.com/pyansys/pymapdl/blob/main/tests/test_math.py>`_ of the 
+**ansys.mapdl.core.math** library is one of the numerous unit tests that you can find in
+the `test directory <https://github.com/pyansys/pymapdl/tree/main/tests>`_ . 
+You'll find examples to understand how you can use the pytest package.
+
+
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+