deprecated_call now uses monkey patching strategy to capture warnings

similar to what we had in 2.7, with a few enhancements

Fix pytest-dev#1190

Author: nicoddemus

_pytest/recwarn.py

@@ -29,29 +29,39 @@ def pytest_namespace():
 
 
 def deprecated_call(func, *args, **kwargs):
-    """ assert that calling ``func(*args, **kwargs)``
-    triggers a DeprecationWarning.
+    """ assert that calling ``func(*args, **kwargs)`` triggers a
+    DeprecationWarning.
+
+    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.
     """
-    l = []
-    oldwarn_explicit = getattr(warnings, 'warn_explicit')
-    def warn_explicit(*args, **kwargs):
-        l.append(args)
-        oldwarn_explicit(*args, **kwargs)
-    oldwarn = getattr(warnings, 'warn')
-    def warn(*args, **kwargs):
-        l.append(args)
-        oldwarn(*args, **kwargs)
+    categories = []
+
+    def warn_explicit(message, category, *args, **kwargs):
+        categories.append(category)
+        old_warn_explicit(message, category, *args, **kwargs)
+
+    def warn(message, category=None, **kwargs):
+        if isinstance(message, Warning):
+            categories.append(message.__class__)
+        else:
+            categories.append(category)
+        old_warn(message, category, *args, **kwargs)
 
+    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 = oldwarn_explicit
-        warnings.warn = oldwarn
-    if not l:
+        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,))
+        raise AssertionError("%r did not produce DeprecationWarning" % (func,))
     return ret
 
 

testing/test_recwarn.py

@@ -72,7 +72,6 @@ def dep(i):
         py.std.warnings.warn("is deprecated", DeprecationWarning)
     return 42
 
-reg = {}
 def dep_explicit(i):
     if i == 0:
         py.std.warnings.warn_explicit("dep_explicit", category=DeprecationWarning,
@@ -123,6 +122,27 @@ def test_deprecated_call_specificity(self):
             with pytest.raises(AssertionError):
                 pytest.deprecated_call(f)
 
+    def test_deprecated_function_already_called(self, testdir):
+        """deprecated_call should be able to catch a call to a deprecated
+        function even if that function has already been called in the same
+        module. See #1190.
+        """
+        testdir.makepyfile("""
+            import warnings
+            import pytest
+
+            def deprecated_function():
+                warnings.warn("deprecated", DeprecationWarning)
+
+            def test_one():
+                deprecated_function()
+
+            def test_two():
+                pytest.deprecated_call(deprecated_function)
+        """)
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines('*=== 2 passed in *===')
+
 
 class TestWarns(object):
     def test_strings(self):