deprecated_call context manager captures warnings already raised

Fix pytest-dev#2469

_pytest/recwarn.py

@@ -27,10 +27,8 @@ def recwarn():
 
 
 def deprecated_call(func=None, *args, **kwargs):
-    """ assert that calling ``func(*args, **kwargs)`` triggers a
-    ``DeprecationWarning`` or ``PendingDeprecationWarning``.
-
-    This function can be used as a context manager::
+    """context manager that can be used to ensure a block of code triggers a
+    ``DeprecationWarning`` or ``PendingDeprecationWarning``::
 
         >>> import warnings
         >>> def api_call_v2():
@@ -40,38 +38,46 @@ def deprecated_call(func=None, *args, **kwargs):
         >>> with deprecated_call():
         ...    assert api_call_v2() == 200
 
-    Note: we cannot use WarningsRecorder here because it is still subject
-    to the mechanism that prevents warnings of the same type from being
-    triggered twice for the same module. See #1190.
+    ``deprecated_call`` can also be used by passing a function and ``*args`` and ``*kwargs``,
+    in which case it will ensure calling ``func(*args, **kwargs)`` produces one of the warnings
+    types above.
     """
     if not func:
-        return WarningsChecker(expected_warning=(DeprecationWarning, PendingDeprecationWarning))
+        return _DeprecatedCallContext()
+    else:
+        with _DeprecatedCallContext():
+            return func(*args, **kwargs)
+
 
-    categories = []
+class _DeprecatedCallContext(object):
+    """Implements the logic to capture deprecation warnings as a context manager."""
 
-    def warn_explicit(message, category, *args, **kwargs):
-        categories.append(category)
+    def __enter__(self):
+        self._captured_categories = []
+        self._old_warn = warnings.warn
+        self._old_warn_explicit = warnings.warn_explicit
+        warnings.warn_explicit = self._warn_explicit
+        warnings.warn = self._warn
+
+    def _warn_explicit(self, message, category, *args, **kwargs):
+        self._captured_categories.append(category)
 
-    def warn(message, category=None, *args, **kwargs):
+    def _warn(self, message, category=None, *args, **kwargs):
         if isinstance(message, Warning):
-            categories.append(message.__class__)
+            self._captured_categories.append(message.__class__)
         else:
-            categories.append(category)
-
-    old_warn = warnings.warn
-    old_warn_explicit = warnings.warn_explicit
-    warnings.warn_explicit = warn_explicit
-    warnings.warn = warn
-    try:
-        ret = func(*args, **kwargs)
-    finally:
-        warnings.warn_explicit = old_warn_explicit
-        warnings.warn = old_warn
-    deprecation_categories = (DeprecationWarning, PendingDeprecationWarning)
-    if not any(issubclass(c, deprecation_categories) for c in categories):
-        __tracebackhide__ = True
-        raise AssertionError("%r did not produce DeprecationWarning" % (func,))
-    return ret
+            self._captured_categories.append(category)
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        warnings.warn_explicit = self._old_warn_explicit
+        warnings.warn = self._old_warn
+
+        if exc_type is None:
+            deprecation_categories = (DeprecationWarning, PendingDeprecationWarning)
+            if not any(issubclass(c, deprecation_categories) for c in self._captured_categories):
+                __tracebackhide__ = True
+                msg = "Did not produce DeprecationWarning or PendingDeprecationWarning"
+                raise AssertionError(msg)
 
 
 def warns(expected_warning, *args, **kwargs):

changelog/2469.bugfix

@@ -0,0 +1,4 @@
+``deprecated_call`` in context-manager form now captures deprecation warnings even if
+the same warning has already been raised. Also, ``deprecated_call`` will always produce
+the same error message (previously it would produce different messages in context-manager vs.
+function-call mode).

testing/test_recwarn.py

@@ -77,7 +77,7 @@ def dep_explicit(self, i):
     def test_deprecated_call_raises(self):
         with pytest.raises(AssertionError) as excinfo:
             pytest.deprecated_call(self.dep, 3, 5)
-        assert str(excinfo).find("did not produce") != -1
+        assert 'Did not produce' in str(excinfo)
 
     def test_deprecated_call(self):
         pytest.deprecated_call(self.dep, 0, 5)
@@ -106,31 +106,54 @@ def test_deprecated_explicit_call(self):
         pytest.deprecated_call(self.dep_explicit, 0)
         pytest.deprecated_call(self.dep_explicit, 0)
 
-    def test_deprecated_call_as_context_manager_no_warning(self):
-        with pytest.raises(pytest.fail.Exception, matches='^DID NOT WARN'):
-            with pytest.deprecated_call():
-                self.dep(1)
+    @pytest.mark.parametrize('mode', ['context_manager', 'call'])
+    def test_deprecated_call_no_warning(self, mode):
+        """Ensure deprecated_call() raises the expected failure when its block/function does
+        not raise a deprecation warning.
+        """
+        def f():
+            pass
+
+        msg = 'Did not produce DeprecationWarning or PendingDeprecationWarning'
+        with pytest.raises(AssertionError, matches=msg):
+            if mode == 'call':
+                pytest.deprecated_call(f)
+            else:
+                with pytest.deprecated_call():
+                    f()
 
     @pytest.mark.parametrize('warning_type', [PendingDeprecationWarning, DeprecationWarning])
     @pytest.mark.parametrize('mode', ['context_manager', 'call'])
-    def test_deprecated_call_modes(self, warning_type, mode):
+    @pytest.mark.parametrize('call_f_first', [True, False])
+    def test_deprecated_call_modes(self, warning_type, mode, call_f_first):
+        """Ensure deprecated_call() captures a deprecation warning as expected inside its
+        block/function.
+        """
         def f():
             warnings.warn(warning_type("hi"))
-
+            return 10
+
+        # ensure deprecated_call() can capture the warning even if it has already been triggered
+        if call_f_first:
+            assert f() == 10
         if mode == 'call':
-            pytest.deprecated_call(f)
+            assert pytest.deprecated_call(f) == 10
         else:
             with pytest.deprecated_call():
-                f()
+                assert f() == 10
 
     def test_deprecated_call_specificity(self):
         other_warnings = [Warning, UserWarning, SyntaxWarning, RuntimeWarning,
                           FutureWarning, ImportWarning, UnicodeWarning]
         for warning in other_warnings:
             def f():
-                py.std.warnings.warn(warning("hi"))
+                warnings.warn(warning("hi"))
+
             with pytest.raises(AssertionError):
                 pytest.deprecated_call(f)
+            with pytest.raises(AssertionError):
+                with pytest.deprecated_call():
+                    f()
 
     def test_deprecated_function_already_called(self, testdir):
         """deprecated_call should be able to catch a call to a deprecated