318: Update Contributors Guide with testing instructions

docs/Contributors_Guide/running_unit_tests_locally.rst

@@ -6,10 +6,55 @@ Running Unit Tests Locally
 Background
 ===========
 
-The METdataio METdbLoad module includes unit tests, found in `METdbload/test/`.
+Unit tests are included in METdataio and all of its sub-modules. The tests are found under the `test/` directory in each module, e.g. `METdbLoad/test/`.
 These tests are run automatically when a pull request is raised on GitHub and must pass before any merge will be considered. 
-When developing new features it is advisable to ensure the tests will pass by running them locally. To do this you must first have either
-a `mysql` or `mariadb` service running and setup with an appropriate user.
+When developing new features it is advisable to ensure the test pass by running them locally against your changes. To do this you must first have either
+a `mysql` or `mariadb` service running and setup with an appropriate user. Although either database can be used, this guide will focus on `mariadb`.
 
-Steps
-=====
+Database Setup
+==============
+
+The setup of `mariadb` will be different depending on the operating system you are running, and the available priviledges. If you encounter issues it is recommended you consult your system administrator
+for support appropriate to your system and environment. For up to date instructions on installing mariadb consult the `MariaDB docs <mariadb.org>`_ or the `MariaDB GitHub page <https://github.com/MariaDB/>`_.
+
+Below is an example setup on CentOS.
+
+1. Install mariadb-server: 
+.. code-block:: console
+  $ sudo yum install mariadb-server
+
+2. start mariadb and change the root password. Note that by default there is no password for the root user:
+.. code-block:: console
+  $ sudo mariadb -u root -p
+  [MariaDB]> ALTER USER 'root'@'localhost' IDENTIFIED BY 'root_password';
+  [MariaDB]> exit;
+
+3. start the mariadb service:
+.. code-block:: console
+  $ sudo systemctl start mariadb
+
+
+Running Tests
+=============
+
+Tests can be run using `pytest`. If required, you can install using either `conda install pytest` or `pip install pytest`.
+.. code-block:: console
+  $ pytest METdbLoad/test/
+
+To check test coverage `conda install pytest-cov`, and using the `--cov` commands. For example:
+
+.. code-block:: console
+  $ pytest METdbLoad/test/ --cov METdbLoad/ush/ --cov-report term-missing
+
+
+Writing Tests
+=============
+
+All Pull Requests that change source code in `METdataio` should include appropriate unit tests. These tests should 
+demonstrate that when the new source code is invoked it produces the desired results. For help with writing tests, and for examples 
+of how to use pytest, refer ot the `pytest documentation <https://docs.pytest.org/>`_.
+
+When writing new tests for `METdataio` you should be familiar with the content of `conftest.py`, noting that each sub module may have it's own `conftest.py`.
+For example, when writing a test for `METdbLoad` you may want to instatiate an empty test database. To do this use the `emptyDB` test fixture, found in `METdbLoad/conftest.py`.
+
+For further examples, refer to the existing tests for each module.