Execute 'async def' test functions

pytest didn't use the result of test functions but `async def` functions
return an awaitable object.

Though `async def` functions were just passed like they don't have any
problem, their codes actually didn't run. For users, it was really hard to
detect the tests really were run or not.

This patch makes to check the result of test functions and if it is an
awaitable object then actually run the functions to ensure its code is
run.

Author: youknowone

_pytest/python.py

@@ -151,7 +151,15 @@ def pytest_pyfunc_call(pyfuncitem):
         testargs = {}
         for arg in pyfuncitem._fixtureinfo.argnames:
             testargs[arg] = funcargs[arg]
-        testfunction(**testargs)
+        testreturn = testfunction(**testargs)
+        if inspect.isawaitable(testreturn):
+            try:
+                import asyncio
+            except ImportError:
+                pass
+            else:
+                loop = asyncio.get_event_loop()
+                loop.run_until_complete(testreturn)
     return True
 
 def pytest_collect_file(path, parent):

testing/test_async.py

@@ -0,0 +1,14 @@
+import sys
+
+import traceback
+import pytest
+
+@pytest.mark.skipif(sys.version_info < (3, 5), reason='async syntax available in Python 3.5+')
+def test_async_function(testdir):
+    testdir.makepyfile("""
+        async def test_async_function_py35():
+            assert False
+    """)
+    # avoid importing asyncio into pytest's own process, which in turn imports logging (#8)
+    result = testdir.runpytest_subprocess()
+    result.stdout.fnmatch_lines(['*1 failed*'])