Allow MarkEvaluator expressions to be unicode

This fixes issue #266.

_pytest/skipping.py

@@ -3,6 +3,12 @@
 import py, pytest
 import sys
 
+# Provide basestring in python3
+try:
+    basestring = basestring
+except NameError:
+    basestring = str
+
 def pytest_addoption(parser):
     group = parser.getgroup("general")
     group.addoption('--runxfail',
@@ -86,7 +92,7 @@ class MarkEvaluator:
                 self.result = False
                 for expr in self.holder.args:
                     self.expr = expr
-                    if isinstance(expr, str):
+                    if isinstance(expr, basestring):
                         result = cached_eval(self.item.config, expr, d)
                     else:
                         pytest.fail("expression is not a string")

testing/test_skipping.py

@@ -39,6 +39,20 @@ class TestEvaluator:
         expl = ev.getexplanation()
         assert expl == "condition: hasattr(os, 'sep')"
 
+    @pytest.mark.skipif('sys.version_info[0] >= 3')
+    def test_marked_one_arg_unicode(self, testdir):
+        item = testdir.getitem("""
+            import pytest
+            @pytest.mark.xyz(u"hasattr(os, 'sep')")
+            def test_func():
+                pass
+        """)
+        ev = MarkEvaluator(item, 'xyz')
+        assert ev
+        assert ev.istrue()
+        expl = ev.getexplanation()
+        assert expl == "condition: hasattr(os, 'sep')"
+
     def test_marked_one_arg_with_reason(self, testdir):
         item = testdir.getitem("""
             import pytest