fix regression reported by dstufft: regression when a 1-tuple ("arg",) is used

for specifying parametrization (the values of the parametrization were passed
nested in a tuple).

CHANGELOG

@@ -8,6 +8,10 @@ Changes between 2.4.0 and 2.4.1
 - fix dotted filename completion when using argcomplete 
   thanks Anthon van der Neuth. (fixes issue361)
 
+- fix regression when a 1-tuple ("arg",) is used for specifying
+  parametrization (the values of the parametrization were passed
+  nested in a tuple).  Thanks Donald Stufft.
+
 - merge doc typo fixes, thanks Andy Dirnberger
 
 Changes between 2.3.5 and 2.4

_pytest/python.py

@@ -710,8 +710,8 @@ class Metafunc(FuncargnamesCompatAttr):
 
         if not isinstance(argnames, (tuple, list)):
             argnames = [x.strip() for x in argnames.split(",") if x.strip()]
-        if len(argnames) == 1:
-            argvalues = [(val,) for val in argvalues]
+            if len(argnames) == 1:
+                argvalues = [(val,) for val in argvalues]
         if not argvalues:
             argvalues = [(_notexists,) * len(argnames)]
 

testing/python/collect.py

@@ -316,6 +316,16 @@ class TestFunction:
         reprec = testdir.inline_run()
         reprec.assertoutcome(skipped=1)
 
+    def test_single_tuple_unwraps_values(self, testdir):
+        testdir.makepyfile("""
+            import pytest
+            @pytest.mark.parametrize(('arg',), [(1,)])
+            def test_function(arg):
+                assert arg == 1
+        """)
+        reprec = testdir.inline_run()
+        reprec.assertoutcome(passed=1)
+
     def test_issue213_parametrize_value_no_equal(self, testdir):
         testdir.makepyfile("""
             import pytest