Warns

AUTHORS

@@ -28,6 +28,7 @@ Eduardo Schettino
 Eric Siegerman
 Florian Bruhin
 Edison Gustavo Muenz
+Eric Hunsberger
 Floris Bruynooghe
 Graham Horler
 Grig Gheorghiu

CHANGELOG

@@ -1,6 +1,9 @@
 2.8.0.dev (compared to 2.7.X)
 -----------------------------
 
+- Add 'warns' to assert that warnings are thrown (like 'raises').
+  Thanks to Eric Hunsberger for the PR.
+
 - Fix #683: Do not apply an already applied mark.  Thanks ojake for the PR.
 
 - Deal with capturing failures better so fewer exceptions get lost to

CONTRIBUTING.rst

@@ -191,6 +191,10 @@ but here is a simple overview:
     $ git commit -a -m "<commit message>"
     $ git push -u
 
+   Make sure you add a CHANGELOG message, and add yourself to AUTHORS. If you
+   are unsure about either of these steps, submit your pull request and we'll
+   help you fix it up.
+
 #. Finally, submit a pull request through the GitHub website:
 
    .. image:: img/pullrequest.png

_pytest/python.py

@@ -1052,8 +1052,8 @@ def getlocation(function, curdir):
 
 # builtin pytest.raises helper
 
-def raises(ExpectedException, *args, **kwargs):
-    """ assert that a code block/function call raises @ExpectedException
+def raises(expected_exception, *args, **kwargs):
+    """ assert that a code block/function call raises @expected_exception
     and raise a failure exception otherwise.
 
     This helper produces a ``py.code.ExceptionInfo()`` object.
@@ -1101,23 +1101,23 @@ def raises(ExpectedException, *args, **kwargs):
 
     """
     __tracebackhide__ = True
-    if ExpectedException is AssertionError:
+    if expected_exception is AssertionError:
         # we want to catch a AssertionError
         # replace our subclass with the builtin one
         # see https://github.com/pytest-dev/pytest/issues/176
         from _pytest.assertion.util import BuiltinAssertionError \
-            as ExpectedException
+            as expected_exception
     msg = ("exceptions must be old-style classes or"
            " derived from BaseException, not %s")
-    if isinstance(ExpectedException, tuple):
-        for exc in ExpectedException:
+    if isinstance(expected_exception, tuple):
+        for exc in expected_exception:
             if not inspect.isclass(exc):
                 raise TypeError(msg % type(exc))
-    elif not inspect.isclass(ExpectedException):
-        raise TypeError(msg % type(ExpectedException))
+    elif not inspect.isclass(expected_exception):
+        raise TypeError(msg % type(expected_exception))
 
     if not args:
-        return RaisesContext(ExpectedException)
+        return RaisesContext(expected_exception)
     elif isinstance(args[0], str):
         code, = args
         assert isinstance(code, str)
@@ -1130,19 +1130,19 @@ def raises(ExpectedException, *args, **kwargs):
             py.builtin.exec_(code, frame.f_globals, loc)
             # XXX didn'T mean f_globals == f_locals something special?
             #     this is destroyed here ...
-        except ExpectedException:
+        except expected_exception:
             return py.code.ExceptionInfo()
     else:
         func = args[0]
         try:
             func(*args[1:], **kwargs)
-        except ExpectedException:
+        except expected_exception:
             return py.code.ExceptionInfo()
     pytest.fail("DID NOT RAISE")
 
 class RaisesContext(object):
-    def __init__(self, ExpectedException):
-        self.ExpectedException = ExpectedException
+    def __init__(self, expected_exception):
+        self.expected_exception = expected_exception
         self.excinfo = None
 
     def __enter__(self):
@@ -1161,7 +1161,7 @@ def __exit__(self, *tp):
                 exc_type, value, traceback = tp
                 tp = exc_type, exc_type(value), traceback
         self.excinfo.__init__(tp)
-        return issubclass(self.excinfo.type, self.ExpectedException)
+        return issubclass(self.excinfo.type, self.expected_exception)
 
 #
 #  the basic pytest Function item
@@ -2123,4 +2123,3 @@ def get_scope_node(node, scope):
             return node.session
         raise ValueError("unknown scope")
     return node.getparent(cls)
-

_pytest/recwarn.py

@@ -1,10 +1,14 @@
 """ recording warnings during test function execution. """
 
+import inspect
+import py
 import sys
 import warnings
+import pytest
 
 
-def pytest_funcarg__recwarn(request):
+@pytest.yield_fixture
+def recwarn(request):
     """Return a WarningsRecorder instance that provides these methods:
 
     * ``pop(category=None)``: return last warning matching the category.
@@ -13,83 +17,169 @@ def pytest_funcarg__recwarn(request):
     See http://docs.python.org/library/warnings.html for information
     on warning categories.
     """
-    if sys.version_info >= (2,7):
-        oldfilters = warnings.filters[:]
-        warnings.simplefilter('default')
-        def reset_filters():
-            warnings.filters[:] = oldfilters
-        request.addfinalizer(reset_filters)
     wrec = WarningsRecorder()
-    request.addfinalizer(wrec.finalize)
-    return wrec
+    with wrec:
+        warnings.simplefilter('default')
+        yield wrec
+
 
 def pytest_namespace():
-    return {'deprecated_call': deprecated_call}
+    return {'deprecated_call': deprecated_call,
+            'warns': warns}
+
 
 def deprecated_call(func, *args, **kwargs):
-    """ assert that calling ``func(*args, **kwargs)``
-    triggers a DeprecationWarning.
+    """Assert that ``func(*args, **kwargs)`` triggers a DeprecationWarning.
     """
-    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)
-
-    warnings.warn_explicit = warn_explicit
-    warnings.warn = warn
-    try:
+    wrec = WarningsRecorder()
+    with wrec:
+        warnings.simplefilter('always')  # ensure all warnings are triggered
         ret = func(*args, **kwargs)
-    finally:
-        warnings.warn_explicit = oldwarn_explicit
-        warnings.warn = oldwarn
-    if not l:
+
+    if not any(r.category is DeprecationWarning for r in wrec):
         __tracebackhide__ = True
-        raise AssertionError("%r did not produce DeprecationWarning" %(func,))
+        raise AssertionError("%r did not produce DeprecationWarning" % (func,))
+
     return ret
 
 
-class RecordedWarning:
-    def __init__(self, message, category, filename, lineno, line):
+def warns(expected_warning, *args, **kwargs):
+    """Assert that code raises a particular class of warning.
+
+    Specifically, the input @expected_warning can be a warning class or
+    tuple of warning classes, and the code must return that warning
+    (if a single class) or one of those warnings (if a tuple).
+
+    This helper produces a list of ``warnings.WarningMessage`` objects,
+    one for each warning raised.
+
+    This function can be used as a context manager, or any of the other ways
+    ``pytest.raises`` can be used::
+
+        >>> with warns(RuntimeWarning):
+        ...    warnings.warn("my warning", RuntimeWarning)
+    """
+    wcheck = WarningsChecker(expected_warning)
+    if not args:
+        return wcheck
+    elif isinstance(args[0], str):
+        code, = args
+        assert isinstance(code, str)
+        frame = sys._getframe(1)
+        loc = frame.f_locals.copy()
+        loc.update(kwargs)
+
+        with wcheck:
+            code = py.code.Source(code).compile()
+            py.builtin.exec_(code, frame.f_globals, loc)
+    else:
+        func = args[0]
+        with wcheck:
+            return func(*args[1:], **kwargs)
+
+
+class RecordedWarning(object):
+    def __init__(self, message, category, filename, lineno, file, line):
         self.message = message
         self.category = category
         self.filename = filename
         self.lineno = lineno
+        self.file = file
         self.line = line
 
-class WarningsRecorder:
-    def __init__(self):
-        self.list = []
-        def showwarning(message, category, filename, lineno, line=0):
-            self.list.append(RecordedWarning(
-                message, category, filename, lineno, line))
-            try:
-                self.old_showwarning(message, category,
-                    filename, lineno, line=line)
-            except TypeError:
-                # < python2.6
-                self.old_showwarning(message, category, filename, lineno)
-        self.old_showwarning = warnings.showwarning
-        warnings.showwarning = showwarning
+
+class WarningsRecorder(object):
+    """A context manager to record raised warnings.
+
+    Adapted from `warnings.catch_warnings`.
+    """
+
+    def __init__(self, module=None):
+        self._module = sys.modules['warnings'] if module is None else module
+        self._entered = False
+        self._list = []
+
+    @property
+    def list(self):
+        """The list of recorded warnings."""
+        return self._list
+
+    def __getitem__(self, i):
+        """Get a recorded warning by index."""
+        return self._list[i]
+
+    def __iter__(self):
+        """Iterate through the recorded warnings."""
+        return iter(self._list)
+
+    def __len__(self):
+        """The number of recorded warnings."""
+        return len(self._list)
 
     def pop(self, cls=Warning):
-        """ pop the first recorded warning, raise exception if not exists."""
-        for i, w in enumerate(self.list):
+        """Pop the first recorded warning, raise exception if not exists."""
+        for i, w in enumerate(self._list):
             if issubclass(w.category, cls):
-                return self.list.pop(i)
+                return self._list.pop(i)
         __tracebackhide__ = True
-        assert 0, "%r not found in %r" %(cls, self.list)
-
-    #def resetregistry(self):
-    #    warnings.onceregistry.clear()
-    #    warnings.__warningregistry__.clear()
+        raise AssertionError("%r not found in warning list" % cls)
 
     def clear(self):
-        self.list[:] = []
+        """Clear the list of recorded warnings."""
+        self._list[:] = []
+
+    def __enter__(self):
+        if self._entered:
+            __tracebackhide__ = True
+            raise RuntimeError("Cannot enter %r twice" % self)
+        self._entered = True
+        self._filters = self._module.filters
+        self._module.filters = self._filters[:]
+        self._showwarning = self._module.showwarning
+
+        def showwarning(message, category, filename, lineno,
+                        file=None, line=None):
+            self._list.append(RecordedWarning(
+                message, category, filename, lineno, file, line))
+
+            # still perform old showwarning functionality
+            self._showwarning(message, category, filename, lineno,
+                              file=file, line=line)
+
+        self._module.showwarning = showwarning
+        return self
+
+    def __exit__(self, *exc_info):
+        if not self._entered:
+            __tracebackhide__ = True
+            raise RuntimeError("Cannot exit %r without entering first" % self)
+        self._module.filters = self._filters
+        self._module.showwarning = self._showwarning
+
+
+class WarningsChecker(WarningsRecorder):
+    def __init__(self, expected_warning=None, module=None):
+        super(WarningsChecker, self).__init__(module=module)
+
+        msg = ("exceptions must be old-style classes or "
+               "derived from Warning, not %s")
+        if isinstance(expected_warning, tuple):
+            for exc in expected_warning:
+                if not inspect.isclass(exc):
+                    raise TypeError(msg % type(exc))
+        elif inspect.isclass(expected_warning):
+            expected_warning = (expected_warning,)
+        elif expected_warning is not None:
+            raise TypeError(msg % type(expected_warning))
+
+        self.expected_warning = expected_warning
+
+    def __exit__(self, *exc_info):
+        super(WarningsChecker, self).__exit__(*exc_info)
 
-    def finalize(self):
-        warnings.showwarning = self.old_showwarning
+        # only check if we're not currently handling an exception
+        if all(a is None for a in exc_info):
+            if self.expected_warning is not None:
+                if not any(r.category in self.expected_warning for r in self):
+                    __tracebackhide__ = True
+                    pytest.fail("DID NOT WARN")

doc/en/assert.txt

@@ -114,6 +114,16 @@ like documenting unfixed bugs (where the test describes what "should" happen)
 or bugs in dependencies.
 
 
+.. _`assertwarns`:
+
+Assertions about expected warnings
+-----------------------------------------
+
+.. versionadded:: 2.8
+
+You can check that code raises a particular warning using
+:ref:`pytest.warns <warns>`.
+
 
 .. _newreport: