Fixed issue where fixtures get called with NOT_USED as a parameter when using a fixture_union. This issue is actually only fixed in @pytest_fixture_plus, if you use @pytest.fixture you have to handle it manually. Fixes #37

Author: Sylvain MARIE

docs/index.md

@@ -240,14 +240,13 @@ The topic has been largely discussed in [pytest-dev](https://github.com/pytest-d
 `fixture_union` is an implementation of this proposal.
 
 ```python
-import pytest
-from pytest_cases import fixture_union
+from pytest_cases import pytest_fixture_plus, fixture_union
 
-@pytest.fixture
+@pytest_fixture_plus
 def first():
     return 'hello'
 
-@pytest.fixture(params=['a', 'b'])
+@pytest_fixture_plus(params=['a', 'b'])
 def second(request):
     return request.param
 
@@ -271,6 +270,7 @@ PASSED
 
 This feature has been tested in very complex cases (several union fixtures, fixtures that are not selected by a given union but that is requested by the test function, etc.). But if you find some strange behaviour don't hesitate to report it in the [issues](https://github.com/smarie/python-pytest-cases/issues) page !
 
+**IMPORTANT** if you do not use `@pytest_fixture_plus` but only `@pytest.fixture`, then you will see that your fixtures are called even when they are not used, with a parameter `NOT_USED`. This symbol is automatically ignored if you use `@pytest_fixture_plus`, otherwise you have to handle it.
 
 !!! note "fixture unions vs. cases" 
     If you're familiar with `pytest-cases` already, you might note `@cases_data` is not so different than a fixture union: we do a union of all case functions. If one day union fixtures are directly supported by `pytest`, we will probably refactor this lib to align all the concepts.

pytest_cases/__init__.py

@@ -1,7 +1,7 @@
 from pytest_cases.case_funcs import case_name, test_target, case_tags, cases_generator
 
 from pytest_cases.main_fixtures import cases_fixture, pytest_fixture_plus, param_fixtures, param_fixture, \
-    fixture_union  # pytest_parametrize_plus
+    fixture_union, NOT_USED  # pytest_parametrize_plus
 
 from pytest_cases.main_params import cases_data, CaseDataGetter, unfold_expected_err, get_all_cases, THIS_MODULE, \
     get_pytest_parametrize_args
@@ -14,7 +14,7 @@
     'case_name',  'test_target', 'case_tags', 'cases_generator',
     # --main_fixtures
     'cases_fixture', 'pytest_fixture_plus', 'param_fixtures', 'param_fixture',  # 'pytest_parametrize_plus',
-    'fixture_union',
+    'fixture_union', 'NOT_USED',
     # --main params
     'cases_data', 'CaseDataGetter', 'THIS_MODULE', 'unfold_expected_err', 'get_all_cases',
     'get_pytest_parametrize_args',

pytest_cases/main_fixtures.py

@@ -7,7 +7,7 @@
 from warnings import warn
 
 from decopatch import function_decorator, DECORATED
-from makefun import with_signature, add_signature_parameters, remove_signature_parameters
+from makefun import with_signature, add_signature_parameters, remove_signature_parameters, wraps
 
 import pytest
 
@@ -274,9 +274,12 @@ def pytest_fixture_plus(scope="function",
     # (1) Collect all @pytest.mark.parametrize markers (including those created by usage of @cases_data)
     parametrizer_marks = get_pytest_parametrize_marks(fixture_func)
     if len(parametrizer_marks) < 1:
-        # -- no parametrization: shortcut
-        fix_creator = pytest.fixture if not isgeneratorfunction(fixture_func) else yield_fixture
-        return fix_creator(scope=scope, autouse=autouse, **kwargs)(fixture_func)
+        return _create_fixture_without_marks(fixture_func, scope, autouse, kwargs)
+    else:
+        if 'params' in kwargs:
+            raise ValueError(
+                "With `pytest_fixture_plus` you cannot mix usage of the keyword argument `params` and of "
+                "the pytest.mark.parametrize marks")
 
     # (2) create the huge "param" containing all params combined
     # --loop (use the same order to get it right)
@@ -355,14 +358,12 @@ def pytest_fixture_plus(scope="function",
     func_needs_request = 'request' in old_sig.parameters
     if not func_needs_request:
         new_sig = add_signature_parameters(new_sig, first=Parameter('request', kind=Parameter.POSITIONAL_OR_KEYWORD))
-    else:
-        new_sig = new_sig
 
     # --common routine used below. Fills kwargs with the appropriate names and values from fixture_params
     def _get_arguments(*args, **kwargs):
-        # kwargs contains request
         request = kwargs['request'] if func_needs_request else kwargs.pop('request')
-
+        if request.param is NOT_USED:
+            return NOT_USED
         # populate the parameters
         if len(params_names_or_name_combinations) == 1:
             _params = [request.param]  # remove the simplification
@@ -383,28 +384,93 @@ def _get_arguments(*args, **kwargs):
     # --Finally create the fixture function, a wrapper of user-provided fixture with the new signature
     if not isgeneratorfunction(fixture_func):
         # normal function with return statement
-        @with_signature(new_sig)
+        @wraps(fixture_func, new_sig=new_sig)
         def wrapped_fixture_func(*args, **kwargs):
-            args, kwargs = _get_arguments(*args, **kwargs)
-            return fixture_func(*args, **kwargs)
+            out = _get_arguments(*args, **kwargs)
+            if out is not NOT_USED:
+                args, kwargs = out
+                return fixture_func(*args, **kwargs)
 
         # transform the created wrapper into a fixture
         fixture_decorator = pytest.fixture(scope=scope, params=final_values, autouse=autouse, ids=final_ids, **kwargs)
         return fixture_decorator(wrapped_fixture_func)
 
     else:
         # generator function (with a yield statement)
-        @with_signature(new_sig)
+        @wraps(fixture_func, new_sig=new_sig)
         def wrapped_fixture_func(*args, **kwargs):
-            args, kwargs = _get_arguments(*args, **kwargs)
-            for res in fixture_func(*args, **kwargs):
-                yield res
+            out = _get_arguments(*args, **kwargs)
+            if out is not NOT_USED:
+                args, kwargs = out
+                for res in fixture_func(*args, **kwargs):
+                    yield res
 
         # transform the created wrapper into a fixture
         fixture_decorator = yield_fixture(scope=scope, params=final_values, autouse=autouse, ids=final_ids, **kwargs)
         return fixture_decorator(wrapped_fixture_func)
 
 
+def _create_fixture_without_marks(fixture_func, scope, autouse, kwargs):
+    """
+    creates a fixture for decorated fixture function `fixture_func`.
+
+    :param fixture_func:
+    :param scope:
+    :param autouse:
+    :param kwargs:
+    :return:
+    """
+    if 'params' not in kwargs:
+        # -- no parametrization: shortcut
+        fix_creator = pytest.fixture if not isgeneratorfunction(fixture_func) else yield_fixture
+        return fix_creator(scope=scope, autouse=autouse, **kwargs)(fixture_func)
+    else:
+        # --create a wrapper where we will be able to auto-detect
+        # TODO we could put this in a dedicated wrapper 'ignore_unsused'..
+
+        old_sig = signature(fixture_func)
+        # add request if needed
+        func_needs_request = 'request' in old_sig.parameters
+        if not func_needs_request:
+            new_sig = add_signature_parameters(old_sig,
+                                               first=Parameter('request', kind=Parameter.POSITIONAL_OR_KEYWORD))
+        else:
+            new_sig = old_sig
+        if not isgeneratorfunction(fixture_func):
+            # normal function with return statement
+            @wraps(fixture_func, new_sig=new_sig)
+            def wrapped_fixture_func(*args, **kwargs):
+                request = kwargs['request'] if func_needs_request else kwargs.pop('request')
+                if request.param is not NOT_USED:
+                    return fixture_func(*args, **kwargs)
+
+            # transform the created wrapper into a fixture
+            fixture_decorator = pytest.fixture(scope=scope, autouse=autouse, **kwargs)
+            return fixture_decorator(wrapped_fixture_func)
+
+        else:
+            # generator function (with a yield statement)
+            @wraps(fixture_func, new_sig=new_sig)
+            def wrapped_fixture_func(*args, **kwargs):
+                request = kwargs['request'] if func_needs_request else kwargs.pop('request')
+                if request.param is not NOT_USED:
+                    for res in fixture_func(*args, **kwargs):
+                        yield res
+
+            # transform the created wrapper into a fixture
+            fixture_decorator = yield_fixture(scope=scope, autouse=autouse, **kwargs)
+            return fixture_decorator(wrapped_fixture_func)
+
+
+class _NotUsed:
+    def __repr__(self):
+        return "<not_used>"
+
+
+NOT_USED = _NotUsed()
+"""Object representing a fixture value when the fixture is not used"""
+
+
 class UnionFixtureConfig:
     def __init__(self, fixtures):
         self.fixtures = fixtures

pytest_cases/plugin.py

@@ -3,7 +3,7 @@
 
 import pytest
 
-from pytest_cases.main_fixtures import UnionFixtureConfig
+from pytest_cases.main_fixtures import UnionFixtureConfig, NOT_USED
 
 try:  # python 3.3+
     from inspect import signature
@@ -473,15 +473,6 @@ def discard_last_id(self):
             callspec._idlist.pop(-1)
 
 
-class _NotUsed:
-    def __repr__(self):
-        return "<not_used>"
-
-
-NOT_USED = _NotUsed()
-"""Object representing a fixture value when the fixture is not used"""
-
-
 class FilteredLeafNode(LeafNode):
     """
     Represents a set of calls for which at least one union fixture has been parametrized.

pytest_cases/tests/fixtures/test_fixtures_union_1simple.py

@@ -1,8 +1,15 @@
-from pytest_cases import param_fixture, fixture_union
-
+from pytest_cases import param_fixture, fixture_union, pytest_fixture_plus
 
 a = param_fixture('a', ['x', 'y'])
-b = param_fixture('b', [1, 2])
+
+
+@pytest_fixture_plus(params=[1, 2])
+def b(request):
+    # make sure that if this is called, then it is for a good reason
+    assert request.param in [1, 2]
+    return request.param
+
+
 c = fixture_union('c', [a, b])
 
 

pytest_cases/tests/fixtures/test_so.py

@@ -0,0 +1,22 @@
+import pytest
+
+from pytest_cases import fixture_union, pytest_fixture_plus, NOT_USED
+
+
+@pytest_fixture_plus(params=[1, 2, 3])
+def lower(request):
+    return "i" * request.param
+
+
+@pytest.fixture(params=[1, 2])
+def upper(request):
+    # this fixture does not use pytest_fixture_plus so we have to explicitly discard the 'not used' cases
+    if request.param is not NOT_USED:
+        return "I" * request.param
+
+
+fixture_union('all', ['lower', 'upper'])
+
+
+def test_all(all):
+    print(all)