Automatically skip slow tests

You can mark a test as slow using:

    @pytest.mark.slow
    def test_something():
        ...

Use the option "--runslow" to tell the test runner to also include slow
tests:
        py.test --runslow ...

tests/conftest.py

@@ -1,5 +1,3 @@
-from collections import namedtuple
-
 import pytest
 
 
@@ -10,3 +8,12 @@ class Object:
 @pytest.fixture
 def object():
     return Object()
+
+
+def pytest_addoption(parser):
+    parser.addoption("--runslow", action="store_true", help="run slow tests")
+
+
+def pytest_runtest_setup(item):
+    if "slow" in item.keywords and not item.config.getoption("--runslow"):
+        pytest.skip("need --runslow option to run")