fix doctest module when a mock object is around

fixes #3456

changelog/3456.bugfix.rst

@@ -0,0 +1 @@
+Extend Doctest-modules to ignore mock objects.

src/_pytest/doctest.py

@@ -3,17 +3,19 @@ from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
 
+import inspect
 import platform
 import sys
 import traceback
+from contextlib import contextmanager
 
 import pytest
 from _pytest._code.code import ExceptionInfo
 from _pytest._code.code import ReprFileLocation
 from _pytest._code.code import TerminalRepr
+from _pytest.compat import safe_getattr
 from _pytest.fixtures import FixtureRequest
 
-
 DOCTEST_REPORT_CHOICE_NONE = "none"
 DOCTEST_REPORT_CHOICE_CDIFF = "cdiff"
 DOCTEST_REPORT_CHOICE_NDIFF = "ndiff"
@@ -346,10 +348,61 @@ def _check_all_skipped(test):
         pytest.skip("all tests skipped by +SKIP option")
 
 
+def _is_mocked(obj):
+    """
+    returns if a object is possibly a mock object by checking the existence of a highly improbable attribute
+    """
+    return (
+        safe_getattr(obj, "pytest_mock_example_attribute_that_shouldnt_exist", None)
+        is not None
+    )
+
+
+@contextmanager
+def _patch_unwrap_mock_aware():
+    """
+    contextmanager which replaces ``inspect.unwrap`` with a version
+    that's aware of mock objects and doesn't recurse on them
+    """
+    real_unwrap = getattr(inspect, "unwrap", None)
+    if real_unwrap is None:
+        yield
+    else:
+
+        def _mock_aware_unwrap(obj, stop=None):
+            if stop is None:
+                return real_unwrap(obj, stop=_is_mocked)
+            else:
+                return real_unwrap(obj, stop=lambda obj: _is_mocked(obj) or stop(obj))
+
+        inspect.unwrap = _mock_aware_unwrap
+        try:
+            yield
+        finally:
+            inspect.unwrap = real_unwrap
+
+
 class DoctestModule(pytest.Module):
     def collect(self):
         import doctest
 
+        class MockAwareDocTestFinder(doctest.DocTestFinder):
+            """
+            a hackish doctest finder that overrides stdlib internals to fix a stdlib bug
+
+            https://github.com/pytest-dev/pytest/issues/3456
+            https://bugs.python.org/issue25532
+            """
+
+            def _find(self, tests, obj, name, module, source_lines, globs, seen):
+                if _is_mocked(obj):
+                    return
+                with _patch_unwrap_mock_aware():
+
+                    doctest.DocTestFinder._find(
+                        self, tests, obj, name, module, source_lines, globs, seen
+                    )
+
         if self.fspath.basename == "conftest.py":
             module = self.config.pluginmanager._importconftest(self.fspath)
         else:
@@ -361,7 +414,7 @@ class DoctestModule(pytest.Module):
                 else:
                     raise
         # uses internal doctest module parsing mechanism
-        finder = doctest.DocTestFinder()
+        finder = MockAwareDocTestFinder()
         optionflags = get_optionflags(self)
         runner = _get_runner(
             verbose=0,

testing/test_doctest.py

@@ -1206,3 +1206,22 @@ class TestDoctestReportingOption(object):
                 "*error: argument --doctest-report: invalid choice: 'obviously_invalid_format' (choose from*"
             ]
         )
+
+
+@pytest.mark.parametrize("mock_module", ["mock", "unittest.mock"])
+def test_doctest_mock_objects_dont_recurse_missbehaved(mock_module, testdir):
+    pytest.importorskip(mock_module)
+    testdir.makepyfile(
+        """
+        from {mock_module} import call
+        class Example(object):
+            '''
+            >>> 1 + 1
+            2
+            '''
+        """.format(
+            mock_module=mock_module
+        )
+    )
+    result = testdir.runpytest("--doctest-modules")
+    result.stdout.fnmatch_lines(["* 1 passed *"])