[doc] improve/expand the Parametrization section (#7156)

docs/source/testing.rst

@@ -494,6 +494,8 @@ Often, there is a need to run the same test multiple times, but with different a
 
 .. code-block:: python
                 
+    # test_this1.py
+    import unittest
     from parameterized import parameterized
     class TestMathUnitTest(unittest.TestCase):
         @parameterized.expand([
@@ -504,7 +506,9 @@ Often, there is a need to run the same test multiple times, but with different a
         def test_floor(self, name, input, expected):
             assert_equal(math.floor(input), expected)
 
-Now this test will be run three times, and you could run just the ``negative`` and ``integer`` sets of params with:
+Now, by default this test will be run 3 times, each time with the last 3 arguments of ``test_floor`` being assigned the corresponding arguments in the parameter list.
+
+and you could run just the ``negative`` and ``integer`` sets of params with:
 
 .. code-block:: bash
 
@@ -512,11 +516,75 @@ Now this test will be run three times, and you could run just the ``negative`` a
 
 or all but ``negative`` sub-tests, with:
 
-
 .. code-block:: bash
 
    pytest -k "not negative" tests/test_mytest.py
 
+Besides using the ``-k`` filter that was just mentioned, you can find out the exact name of each sub-test and run any or all of them using their exact names. 
+        
+.. code-block:: bash
+                
+    pytest test_this1.py --collect-only -q
+
+and it will list:
+                
+.. code-block:: bash
+
+    test_this1.py::TestMathUnitTest::test_floor_0_negative
+    test_this1.py::TestMathUnitTest::test_floor_1_integer
+    test_this1.py::TestMathUnitTest::test_floor_2_large_fraction
+
+So now you can run just 2 specific sub-tests:
+
+.. code-block:: bash
+
+    pytest test_this1.py::TestMathUnitTest::test_floor_0_negative  test_this1.py::TestMathUnitTest::test_floor_1_integer
+   
+The module `parameterized <https://pypi.org/project/parameterized/>`__ which is already in the developer dependencies of ``transformers`` works for both: ``unittests`` and ``pytest`` tests.
+
+If, however, the test is not a ``unittest``, you may use ``pytest.mark.parametrize`` (or you may see it being used in some existing tests, mostly under ``examples``).
+
+Here is the same example, this time using ``pytest``'s ``parametrize`` marker:
+
+.. code-block:: python
+
+    # test_this2.py
+    import pytest
+    @pytest.mark.parametrize(
+        "name, input, expected",
+        [
+            ("negative", -1.5, -2.0),
+            ("integer", 1, 1.0),
+            ("large fraction", 1.6, 1),
+        ],
+    )
+    def test_floor(name, input, expected):
+        assert_equal(math.floor(input), expected)
+
+Same as with ``parameterized``, with ``pytest.mark.parametrize`` you can have a fine control over which sub-tests are run, if the ``-k`` filter doesn't do the job. Except, this parametrization function creates a slightly different set of names for the sub-tests. Here is what they look like:
+        
+.. code-block:: bash
+                
+    pytest test_this2.py --collect-only -q
+
+and it will list:
+                
+.. code-block:: bash
+
+    test_this2.py::test_floor[integer-1-1.0]
+    test_this2.py::test_floor[negative--1.5--2.0]
+    test_this2.py::test_floor[large fraction-1.6-1]       
+
+So now you can run just the specific test:
+
+.. code-block:: bash
+
+    pytest test_this2.py::test_floor[negative--1.5--2.0] test_this2.py::test_floor[integer-1-1.0]
+
+as in the previous example.
+
+    
+
 Temporary files and directories
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~