Usin pytest instead of run-tests mentions

Signed-off-by: Pradyot Ranjan <[email protected]>

docs/source/user_guide/installation/install-from-source.rst

@@ -237,31 +237,27 @@ Finally, to run the unit and the integration suites sequentially, use
 
 	nox -s tests
 
-Using the test runner
+Using pytest
 ~~~~~~~~~~~~~~~~~~~~~~
 
 You can run unit tests for PyBaMM using
 
 .. code:: bash
 
 	  # in the PyBaMM/ directory
-	  nox -s unit
+	  pytest -m unit
 
 
-The above starts a sub-process using the current python interpreter (i.e. using your current
-Python environment) and run the unit tests. This can take a few minutes.
+The above uses pytest (in your current
+Python environment) to run the unit tests. This can take a few minutes.
 
-You can also use the test runner to run the doctests:
+You can also use pytest to run the doctests:
 
 .. code:: bash
 
-	  nox -s unit
+	  pytest --doctest-plus src
 
-There is more to the PyBaMM test runner. To see a list of all options, type
-
-.. code:: bash
-
-	  nox --list
+Refer to the `testing <https://docs.pybamm.org/en/stable/source/user_guide/contributing.html#testing>`_ docs to find out more ways to test PyBaMM using pytest.
 
 How to build the PyBaMM documentation
 -------------------------------------