Use inspect to properly detect generators. Fixes #2129

CHANGELOG.rst

@@ -3,7 +3,8 @@
 
 *
 
-*
+* pytest no longer recognizes coroutine functions as yield tests (`#2129`_).
+  Thanks to `@malinoff`_ for the PR.
 
 *
 
@@ -12,6 +13,9 @@
 *
 
 
+.. _@malinoff: https://github.com/malinoff
+
+.. _#2129: https://github.com/pytest-dev/pytest/issues/2129
 
 3.0.5 (2016-12-05)
 ==================

_pytest/compat.py

@@ -19,6 +19,7 @@
     # Only available in Python 3.4+ or as a backport
     enum = None
 
+
 _PY3 = sys.version_info > (3, 0)
 _PY2 = not _PY3
 
@@ -42,11 +43,18 @@ def _format_args(func):
 
 
 def is_generator(func):
-    try:
-        return _pytest._code.getrawcode(func).co_flags & 32 # generator function
-    except AttributeError: # builtin functions have no bytecode
-        # assume them to not be generators
-        return False
+    genfunc = inspect.isgeneratorfunction(func)
+    return genfunc and not iscoroutinefunction(func)
+
+
+def iscoroutinefunction(func):
+    """Return True if func is a decorated coroutine function.
+
+    Note: copied and modified from Python 3.5's builtin couroutines.py to avoid import asyncio directly,
+    which in turns also initializes the "logging" module as side-effect (see issue #8).
+    """
+    return (getattr(func, '_is_coroutine', False) or
+           (hasattr(inspect, 'iscoroutinefunction') and inspect.iscoroutinefunction(func)))
 
 
 def getlocation(function, curdir):

testing/test_compat.py

@@ -0,0 +1,50 @@
+import sys
+
+import pytest
+from _pytest.compat import is_generator
+
+
+def test_is_generator():
+    def zap():
+        yield
+
+    def foo():
+        pass
+
+    assert is_generator(zap)
+    assert not is_generator(foo)
+
+
+@pytest.mark.skipif(sys.version_info < (3, 4), reason='asyncio available in Python 3.4+')
+def test_is_generator_asyncio(testdir):
+    testdir.makepyfile("""
+        from _pytest.compat import is_generator
+        import asyncio
+        @asyncio.coroutine
+        def baz():
+            yield from [1,2,3]
+
+        def test_is_generator_asyncio():
+            assert not is_generator(baz)
+    """)
+    # avoid importing asyncio into pytest's own process, which in turn imports logging (#8)
+    result = testdir.runpytest_subprocess()
+    result.stdout.fnmatch_lines(['*1 passed*'])
+
+
+@pytest.mark.skipif(sys.version_info < (3, 5), reason='async syntax available in Python 3.5+')
+def test_is_generator_async_syntax(testdir):
+    testdir.makepyfile("""
+        from _pytest.compat import is_generator
+        def test_is_generator_py35():
+            async def foo():
+                await foo()
+
+            async def bar():
+                pass
+
+            assert not is_generator(foo)
+            assert not is_generator(bar)
+    """)
+    result = testdir.runpytest()
+    result.stdout.fnmatch_lines(['*1 passed*'])