Add a default value to CallInfo.result

changelog/3554.bugfix

@@ -0,0 +1 @@
+Allow CallInfo to have an unfinished state represented by having a None value in the result attribute.

src/_pytest/runner.py

@@ -194,6 +194,7 @@ class CallInfo(object):
         #: "teardown", "memocollect"
         self.when = when
         self.start = time()
+        self.result = None
         try:
             self.result = func()
         except KeyboardInterrupt:

testing/test_runner.py

@@ -473,7 +473,7 @@ def test_callinfo():
     assert "result" in repr(ci)
     ci = runner.CallInfo(lambda: 0 / 0, "123")
     assert ci.when == "123"
-    assert not hasattr(ci, "result")
+    assert ci.result is None
     assert ci.excinfo
     assert "exc" in repr(ci)