Update parametrize.rst

Add an example for enforcing explicit argument declaration
References pytest-dev#5712

doc/en/example/parametrize.rst

@@ -396,6 +396,31 @@ The result of this test will be successful:
 
     ========================== no tests ran in 0.12s ===========================
 
+Note, that each argument in `parametrize` list should be explicitly declared in
+python test function or via `indirect`. E.g. the following test will not run:
+
+.. code-block:: python
+
+    # content of test_explicit_argnames.py
+
+    import pytest
+
+
+    @pytest.fixture
+    def fixture(argument):
+        return argument
+
+
+    @pytest.mark.parametrize("argument", ["foobar"])
+    def test_explicit(fixture):
+        assert "foobar" == fixture
+    # should be either test_explicit(fixture, argument) or
+    #
+    #@pytest.mark.parametrize("argument", ['foobar'], indirect=['argument'])
+    #def test_explicit(fixture)
+    #or
+    #@pytest.mark.parametrize("argument", ['foobar'], indirect=True)
+    #def test_explicit(fixture)
 .. regendoc:wipe
 
 Parametrizing test methods through per-class configuration