Add 'named arguments must follow bare *' issue and a few conftest tweaks.

test/normalizer_issue_files/python3.py

@@ -79,3 +79,12 @@ def b(a:int=1):
 
 if alpha[:-i]:
     *a, b = (1, 2, 3)
+
+
+# Named only arguments
+def foo(*, asdf):
+    pass
+
+
+def foo2(bar, *, asdf=2):
+    pass

test/test_python_errors.py

@@ -174,3 +174,12 @@ def test_future_import_first():
     assert is_issue('"";1\n' + i1)
     assert is_issue('""\n%s\nfrom x import a\n%s', i1, i2)
     assert is_issue('%s\n""\n%s', i1, i2)
+
+
+def test_named_argument_issues(works_not_in_py):
+    message = works_not_in_py.get_error_message('def foo(*): pass')
+    if works_not_in_py.version.startswith('2'):
+        message
+
+    works_not_in_py.assert_no_error_in_passing('def foo(*, name): pass')
+    works_not_in_py.assert_no_error_in_passing('def foo(bar, *, name=1): pass')