Move compat tests to a single file using testdir

This avoids having to resort to skipping modules in conftest.py file and avoids flake8 errors

testing/test_compat.py

@@ -1,3 +1,6 @@
+import sys
+
+import pytest
 from _pytest.compat import is_generator
 
 
@@ -10,3 +13,37 @@ def foo():
 
     assert is_generator(zap)
     assert not is_generator(foo)
+
+
+def test_is_generator_asyncio(testdir):
+    pytest.importorskip('asyncio')
+    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)
+    """)
+    result = testdir.runpytest()
+    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*'])