introduce the pytest_configure_funcargs hook for better control on funcarg instanciation/configuration

_pytest/hookspec.py

@@ -115,6 +115,9 @@ pytest_pyfunc_call.firstresult = True
 def pytest_generate_tests(metafunc):
     """ generate (multiple) parametrized calls to a test function."""
 
+def pytest_configure_funcargs(request):
+    """ configure funcargs """
+
 # -------------------------------------------------------------------------
 # generic runtest related hooks
 # -------------------------------------------------------------------------

_pytest/python.py

@@ -500,6 +500,16 @@ def fillfuncargs(function):
     request = FuncargRequest(pyfuncitem=function)
     request._fillfuncargs()
 
+def pytest_configure_funcargs(request):
+    argnames = getfuncargnames(request.function)
+    if argnames:
+        item = request._pyfuncitem
+        assert not getattr(item, '_args', None), (
+                "yielded functions cannot have funcargs")
+        for argname in argnames:
+            if argname not in item.funcargs:
+                item.funcargs[argname] = request.getfuncargvalue(argname)
+
 _notexists = object()
 class CallSpec:
     def __init__(self, funcargs, id, param):
@@ -621,14 +631,6 @@ class FuncargRequest:
         """ the file system path of the test module which collected this test. """
         return self._pyfuncitem.fspath
 
-    def _fillfuncargs(self):
-        argnames = getfuncargnames(self.function)
-        if argnames:
-            assert not getattr(self._pyfuncitem, '_args', None), (
-                "yielded functions cannot have funcargs")
-        for argname in argnames:
-            if argname not in self._pyfuncitem.funcargs:
-                self._pyfuncitem.funcargs[argname] = self.getfuncargvalue(argname)
 
 
     def applymarker(self, marker):
@@ -700,6 +702,9 @@ class FuncargRequest:
             self._currentarg = oldarg
         return res
 
+    def _fillfuncargs(self):
+        self.config.hook.pytest_configure_funcargs.pcall(self._plugins, request=self)
+
     def _getscopeitem(self, scope):
         if scope == "function":
             return self._pyfuncitem

doc/funcargs.txt

@@ -115,6 +115,9 @@ think of as "resources").
 .. _`funcarg factory`:
 .. _factory:
 
+
+
+
 The funcarg **request** object
 =============================================
 
@@ -140,6 +143,16 @@ factory and provides access to test configuration and context:
 .. _`parametrizing-tests`:
 .. _`parametrized test functions`:
 
+
+Reconfiguring funcargs in a test's setup
+========================================
+
+Sometimes there is need to do additional funcarg setup steps
+which are outside of the normal setup and involve more than just one funcarg.
+For that reason the ``pytest_configure_funcargs(request)`` hook
+is called to implement and extend the funcarg filling mechanism.
+
+
 Parametrizing multiple calls to a test function
 ===========================================================
 

testing/test_python.py

@@ -606,6 +606,22 @@ class TestFillFuncArgs:
         fillfuncargs(item)
         assert len(item.funcargs) == 1
 
+    def test_configure_hook(self, testdir):
+        item = testdir.getitem("def test_func(some, other=20): pass")
+        class Provider:
+            def pytest_funcarg__some(self, request):
+                return []
+            def pytest_configure_funcargs(self, request):
+                request.getfuncargvalue('some').append(1)
+        item.config.pluginmanager.register(Provider())
+        if hasattr(item, '_args'):
+            del item._args
+        from _pytest.python import fillfuncargs
+        fillfuncargs(item)
+        assert len(item.funcargs) == 1
+        assert item.funcargs['some'] == [1]
+
+
 class TestRequest:
     def test_request_attributes(self, testdir):
         item = testdir.getitem("""