Added test for the error with pytest 2, and improve readability of the section raising it

Author: Sylvain MARIE

pytest_cases/common.py

@@ -232,12 +232,15 @@ def get_pytest_parametrize_marks(f):
             # mark_info.args contains a list of (name, values)
             if len(mark_info.args) % 2 != 0:
                 raise ValueError("internal pytest compatibility error - please report")
-            nb_parameters = len(mark_info.args) // 2
-            if nb_parameters > 1 and len(mark_info.kwargs) > 0:
+            nb_parametrize_decorations = len(mark_info.args) // 2
+            if nb_parametrize_decorations > 1 and len(mark_info.kwargs) > 0:
                 raise ValueError("Unfortunately with this old pytest version it is not possible to have several "
-                                 "parametrization decorators")
+                                 "parametrization decorators while specifying **kwargs, as all **kwargs are "
+                                 "merged, leading to inconsistent results. Either upgrade pytest, remove the **kwargs,"
+                                 "or merge all the @parametrize decorators into a single one. **kwargs: %s"
+                                 % mark_info.kwargs)
             res = []
-            for i in range(nb_parameters):
+            for i in range(nb_parametrize_decorations):
                 param_name, param_values = mark_info.args[2*i:2*(i+1)]
                 res.append(_ParametrizationMark(_LegacyMark(param_name, param_values, **mark_info.kwargs)))
             return tuple(res)

pytest_cases/tests/fixtures/test_fixtures_parametrize.py

@@ -27,12 +27,22 @@ def test_synthesis(module_results_dct):
 
 
 # pytest.param - not available in all versions
-if LooseVersion(pytest.__version__) >= LooseVersion('3.0.0'):
+if LooseVersion(pytest.__version__) < LooseVersion('3.2.0'):
     # with pytest < 3.2.0 we
     # - would have to merge all parametrize marks if we wish to pass a kwarg (here, ids)
     # - cannot use pytest.param as it is not taken into account
     # > no go
 
+    def test_warning_pytest2():
+        with pytest.raises(ValueError) as exc_info:
+            @pytest_fixture_plus
+            @pytest.mark.parametrize("arg2", [0], ids=str)
+            @pytest.mark.parametrize("arg1", [1])
+            def a(arg1, arg2):
+                return arg1, arg2
+        assert "Unfortunately with this old pytest version it" in str(exc_info.value)
+
+else:
     @pytest_fixture_plus
     @pytest.mark.parametrize("arg3", [pytest.param(0, id='!0!')], ids=str)
     @pytest.mark.parametrize("arg1, arg2", [