move marker transfer to _pytest.mark

_pytest/mark.py

@@ -389,3 +389,32 @@ class MarkInfo(object):
 
 
 MARK_GEN = MarkGenerator()
+
+
+def _marked(func, mark):
+    """ Returns True if :func: is already marked with :mark:, False otherwise.
+    This can happen if marker is applied to class and the test file is
+    invoked more than once.
+    """
+    try:
+        func_mark = getattr(func, mark.name)
+    except AttributeError:
+        return False
+    return mark.args == func_mark.args and mark.kwargs == func_mark.kwargs
+
+
+def transfer_markers(funcobj, cls, mod):
+    # XXX this should rather be code in the mark plugin or the mark
+    # plugin should merge with the python plugin.
+    for holder in (cls, mod):
+        try:
+            pytestmark = holder.pytestmark
+        except AttributeError:
+            continue
+        if isinstance(pytestmark, list):
+            for mark in pytestmark:
+                if not _marked(funcobj, mark):
+                    mark(funcobj)
+        else:
+            if not _marked(funcobj, pytestmark):
+                pytestmark(funcobj)