Explain a bad scope value to the user

AUTHORS

@@ -127,6 +127,7 @@ Ted Xiao
 Thomas Grainger
 Tom Viner
 Trevor Bekolay
+Tyler Goodlet
 Vasily Kuznetsov
 Wouter van Ackooy
 Xuecong Liao

CHANGELOG.rst

@@ -16,18 +16,21 @@
   in Python 3 (`#1944`_).
   Thanks `@axil`_ for the PR.
 
-*
+* Explain a bad scope value passed to ``@fixture`` declarations or
+  a ``MetaFunc.parametrize()`` call. Thanks `@tgoodlet`_ for the PR.
 
 
 .. _@philpep: https://github.com/philpep
 .. _@raquel-ucl: https://github.com/raquel-ucl
 .. _@axil: https://github.com/axil
+.. _@tgoodlet: https://github.com/tgoodlet
 
 .. _#1905: https://github.com/pytest-dev/pytest/issues/1905
 .. _#1934: https://github.com/pytest-dev/pytest/issues/1934
 .. _#1944: https://github.com/pytest-dev/pytest/issues/1944
 
 
+
 3.0.2
 =====
 

_pytest/fixtures.py

@@ -599,12 +599,29 @@ class ScopeMismatchError(Exception):
     which has a lower scope (e.g. a Session one calls a function one)
     """
 
+
 scopes = "session module class function".split()
 scopenum_function = scopes.index("function")
+
+
 def scopemismatch(currentscope, newscope):
     return scopes.index(newscope) > scopes.index(currentscope)
 
 
+def scope2index(scope, descr, where=None):
+    """Look up the index of ``scope`` and raise a descriptive value error
+    if not defined.
+    """
+    try:
+        return scopes.index(scope)
+    except ValueError:
+        raise ValueError(
+            "{0} {1}has an unsupported scope value '{2}'".format(
+                descr, 'from {0} '.format(where) if where else '',
+                scope)
+        )
+
+
 class FixtureLookupError(LookupError):
     """ could not return a requested Fixture (missing or invalid). """
     def __init__(self, argname, request, msg=None):
@@ -703,6 +720,7 @@ def call_fixture_func(fixturefunc, request, kwargs):
         res = fixturefunc(**kwargs)
     return res
 
+
 class FixtureDef:
     """ A container for a factory definition. """
     def __init__(self, fixturemanager, baseid, argname, func, scope, params,
@@ -713,7 +731,11 @@ class FixtureDef:
         self.func = func
         self.argname = argname
         self.scope = scope
-        self.scopenum = scopes.index(scope or "function")
+        self.scopenum = scope2index(
+            scope or "function",
+            descr='fixture {0}'.format(func.__name__),
+            where=baseid
+        )
         self.params = params
         startindex = unittest and 1 or None
         self.argnames = getfuncargnames(func, startindex=startindex)

_pytest/python.py

@@ -770,7 +770,7 @@ class Metafunc(fixtures.FuncargnamesCompatAttr):
             It will also override any fixture-function defined scope, allowing
             to set a dynamic scope using test context or configuration.
         """
-        from _pytest.fixtures import scopes
+        from _pytest.fixtures import scope2index
         from _pytest.mark import extract_argvalue
         from py.io import saferepr
 
@@ -799,7 +799,8 @@ class Metafunc(fixtures.FuncargnamesCompatAttr):
         if scope is None:
             scope = _find_parametrized_scope(argnames, self._arg2fixturedefs, indirect)
 
-        scopenum = scopes.index(scope)
+        scopenum = scope2index(
+            scope, descr='call to {0}'.format(self.parametrize))
         valtypes = {}
         for arg in argnames:
             if arg not in self.fixturenames:

testing/python/fixture.py

@@ -1063,6 +1063,22 @@ class TestFixtureUsages:
             "*1 error*"
         ])
 
+    def test_invalid_scope(self, testdir):
+        testdir.makepyfile("""
+            import pytest
+            @pytest.fixture(scope="functions")
+            def badscope():
+                pass
+
+            def test_nothing(badscope):
+                pass
+        """)
+        result = testdir.runpytest_inprocess()
+        result.stdout.fnmatch_lines(
+            ("*ValueError: fixture badscope from test_invalid_scope.py has an unsupported"
+             " scope value 'functions'")
+        )
+
     def test_funcarg_parametrized_and_used_twice(self, testdir):
         testdir.makepyfile("""
             import pytest

testing/python/metafunc.py

@@ -96,6 +96,14 @@ class TestMetafunc:
         pytest.raises(ValueError, lambda: metafunc.parametrize("y", [5,6]))
         pytest.raises(ValueError, lambda: metafunc.parametrize("y", [5,6]))
 
+    def test_parametrize_bad_scope(self, testdir):
+        def func(x): pass
+        metafunc = self.Metafunc(func)
+        try:
+            metafunc.parametrize("x", [1], scope='doggy')
+        except ValueError as ve:
+            assert "has an unsupported scope value 'doggy'" in str(ve)
+
     def test_parametrize_and_id(self):
         def func(x, y): pass
         metafunc = self.Metafunc(func)