Move "only" directive tests to a seperate test root.

tests/util.py

@@ -30,7 +30,7 @@ from nose import tools, SkipTest
 
 
 __all__ = [
-    'test_root', 'raises', 'raises_msg',
+    'test_root', 'test_roots', 'raises', 'raises_msg',
     'skip_if', 'skip_unless', 'skip_unless_importable', 'Struct',
     'ListOutput', 'TestApp', 'with_app', 'gen_with_app',
     'path', 'with_tempdir', 'write_file',
@@ -39,6 +39,7 @@ __all__ = [
 
 
 test_root = path(__file__).parent.joinpath('root').abspath()
+test_roots = path(__file__).parent.joinpath('roots').abspath()
 
 
 def _excstr(exc):
@@ -153,6 +154,8 @@ class TestApp(application.Sphinx):
             self.cleanup_trees.insert(0, outdir)
         if doctreedir is None:
             doctreedir = srcdir.joinpath(srcdir, self.builddir, 'doctrees')
+            if not doctreedir.isdir():
+                doctreedir.makedirs()
             if cleanenv:
                 self.cleanup_trees.insert(0, doctreedir)
         if confoverrides is None: