added documentation for running specific tests (#561)

* added documentation for running specific tests

* added more info on running specific unit tests

* minor fixes

* Update contributing.rst

Author: joaquinvanschoren

doc/contributing.rst

@@ -98,7 +98,7 @@ execute
     python setup.py install
 
 Testing
-~~~~~~~
+=======
 
 From within the directory of the cloned package, execute:
 
@@ -108,6 +108,56 @@ From within the directory of the cloned package, execute:
 
 .. _extending:
 
+Executing a specific test can be done by specifying the module, test case, and test.  
+To obtain a hierarchical list of all tests, run
+
+.. code:: bash
+
+    pytest --collect-only
+
+.. _extending:
+
+.. code:: bash
+
+    <Module 'tests/test_datasets/test_dataset.py'>
+      <UnitTestCase 'OpenMLDatasetTest'>
+        <TestCaseFunction 'test_dataset_format_constructor'>
+        <TestCaseFunction 'test_get_data'>
+        <TestCaseFunction 'test_get_data_rowid_and_ignore_and_target'>
+        <TestCaseFunction 'test_get_data_with_ignore_attributes'>
+        <TestCaseFunction 'test_get_data_with_rowid'>
+        <TestCaseFunction 'test_get_data_with_target'>
+      <UnitTestCase 'OpenMLDatasetTestOnTestServer'>
+        <TestCaseFunction 'test_tagging'>
+        
+.. _extending:
+
+To run a specific module, add the module name, for instance:
+
+.. code:: bash
+
+    pytest tests/test_datasets/test_dataset.py
+
+.. _extending:
+
+To run a specific unit test case, add the test case name, for instance:
+
+.. code:: bash
+
+    pytest tests/test_datasets/test_dataset.py::OpenMLDatasetTest
+
+.. _extending:
+
+To run a specific unit test, add the test name, for instance:
+
+.. code:: bash
+
+    pytest tests/test_datasets/test_dataset.py::OpenMLDatasetTest::test_get_data
+
+.. _extending:
+
+Happy testing!
+
 Connecting new machine learning libraries
 =========================================