Create existingtestsuite.rst

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+Using pytest with an existing test suite
+===========================================
+
+Pytest can be used with most existing test suites, but it's 
+behavior differs from other test runners such as :ref:`nose` or 
+Python's default unittest framework. 
+
+Before using this section you will want to :ref:`getting-started <install pytest>`.
+
+Running an existing test suite with pytest
+---------------------------------------------
+
+Say you want to contribute to an existing repository somewhere.  
+After pulling the code into your development space using some 
+flavor of version control and (optionally) setting up a virtualenv
+you will want to run::
+    
+    cd <repository>
+    pip install -e .  # Environment dependent alternatives include 
+                      # 'python setup.py develop' and 'conda develop' 
+
+in your project root.  This will set up a symlink to your code in
+site-packages, allowing you to edit your code while your tests
+run against it as if it were installed.
+
+Setting up your project in development mode lets you avoid having to 
+reinstall every time you want to run your tests, and is less brittle than 
+mucking about with sys.path to point your tests at local code.
+
+Also consider using Tox - https://tox.readthedocs.io/en/latest/
+
+.. include:: links.inc