Improved error message when something that is not a fixture is used in unpack_fixture or fixture_union. Fixed #75

`get_fixture_name` can now receive a string.

Author: Sylvain MARIE

pytest_cases/common.py

@@ -3,6 +3,11 @@
 except ImportError:
     from funcsigs import signature
 
+try:
+    from typing import Union, Callable, Any
+except ImportError:
+    pass
+
 from distutils.version import LooseVersion
 from warnings import warn
 
@@ -25,14 +30,50 @@ def remove_duplicates(lst):
             if item not in dset and not dset.add(item)]
 
 
-def get_fixture_name(fixture_fun):
+def is_fixture(fixture_fun  # type: Any
+               ):
+    """
+    Returns True if the provided function is a fixture
+
+    :param fixture_fun:
+    :return:
     """
-    Internal utility to retrieve the fixture name corresponding to the given fixture function .
+    try:
+        # noinspection PyStatementEffect
+        fixture_fun._pytestfixturefunction
+        return True
+    except AttributeError:
+        # not a fixture ?
+        return False
+
+
+def assert_is_fixture(fixture_fun  # type: Any
+                      ):
+    """
+    Raises a ValueError if the provided fixture function is not a fixture.
+
+    :param fixture_fun:
+    :return:
+    """
+    if not is_fixture(fixture_fun):
+        raise ValueError("The provided fixture function does not seem to be a fixture: %s. Did you properly decorate "
+                         "it ?" % fixture_fun)
+
+
+def get_fixture_name(fixture_fun  # type: Union[str, Callable]
+                     ):
+    """
+    Internal utility to retrieve the fixture name corresponding to the given fixture function.
     Indeed there is currently no pytest API to do this.
 
+    Note: this function can receive a string, in which case it is directly returned.
+
     :param fixture_fun:
     :return:
     """
+    if isinstance(fixture_fun, string_types):
+        return fixture_fun
+    assert_is_fixture(fixture_fun)
     try:  # pytest 3
         custom_fixture_name = fixture_fun._pytestfixturefunction.name
     except AttributeError:
@@ -62,8 +103,7 @@ def get_fixture_scope(fixture_fun):
     :param fixture_fun:
     :return:
     """
-    # try:
-    #     # pytest 3
+    assert_is_fixture(fixture_fun)
     return fixture_fun._pytestfixturefunction.scope
     # except AttributeError:
     #     # pytest 2

pytest_cases/main_fixtures.py

@@ -94,11 +94,10 @@ def _unpack_fixture(caller_module, argnames, fixture):
     argnames_lst = get_param_argnames_as_list(argnames)
 
     # possibly get the source fixture name if the fixture symbol was provided
+    source_f_name = get_fixture_name(fixture)
     if not isinstance(fixture, string_types):
-        source_f_name = get_fixture_name(fixture)
         scope = get_fixture_scope(fixture)
     else:
-        source_f_name = fixture
         # we dont have a clue about the real scope, so lets use function scope
         scope = 'function'
 
@@ -911,7 +910,7 @@ def _fixture_union(caller_module,
     f_names = []
     for f in fixtures:
         # possibly get the fixture name if the fixture symbol was provided
-        f_names.append(get_fixture_name(f) if not isinstance(f, string_types) else f)
+        f_names.append(get_fixture_name(f))
 
     if len(f_names) < 1:
         raise ValueError("Empty fixture unions are not permitted")
@@ -981,7 +980,7 @@ def _fixture_product(caller_module, name, fixtures_or_values, fixture_positions,
         # possibly get the fixture name if the fixture symbol was provided
         f = fixtures_or_values[f_pos]
         # and remember the position in the tuple
-        f_names[f_pos] = get_fixture_name(f) if not isinstance(f, string_types) else f
+        f_names[f_pos] = get_fixture_name(f)
 
     # remove duplicates by making it an ordered set
     all_names = remove_duplicates((n for n in f_names if n is not None))