add matching the error message to pytest.raises

Author: Kriechi

CHANGELOG.rst

@@ -13,6 +13,9 @@ New Features
 * ``pytest.warns`` now checks for subclass relationship rather than
   class equality. Thanks `@lesteve`_ for the PR (`#2166`_)
 
+* ``pytest.raises`` now assert that the error message contains a certain text
+  with the `match_info` keyword argument. Thanks `@Kriechi`_ for the PR.
+
 
 Changes
 -------
@@ -56,6 +59,7 @@ Changes
 .. _@fogo: https://github.com/fogo
 .. _@mandeep: https://github.com/mandeep
 .. _@unsignedint: https://github.com/unsignedint
+.. _@Kriechi: https://github.com/Kriechi
 
 .. _#1512: https://github.com/pytest-dev/pytest/issues/1512
 .. _#1874: https://github.com/pytest-dev/pytest/pull/1874

_pytest/python.py

@@ -1145,6 +1145,12 @@ def raises(expected_exception, *args, **kwargs):
            ...
            >>> assert str(exc_info.value) == "value must be <= 10"
 
+    Or you can use the keyword argument ``match_info`` to assert that the
+    exception contains a certain text::
+
+        >>> with raises(ValueError, match_info='must be 0'):
+        ...     if value != 0:
+        ...         raise ValueError("value must be 0 or None")
 
     Or you can specify a callable by passing a to-be-called lambda::
 
@@ -1194,11 +1200,15 @@ def raises(expected_exception, *args, **kwargs):
         raise TypeError(msg % type(expected_exception))
 
     message = "DID NOT RAISE {0}".format(expected_exception)
+    match_info = None
 
     if not args:
         if "message" in kwargs:
             message = kwargs.pop("message")
-        return RaisesContext(expected_exception, message)
+        if "match_info" in kwargs:
+            match_info = kwargs.pop("match_info")
+            message += " with text '{0}'".format(match_info)
+        return RaisesContext(expected_exception, message, match_info)
     elif isinstance(args[0], str):
         code, = args
         assert isinstance(code, str)
@@ -1222,9 +1232,10 @@ def raises(expected_exception, *args, **kwargs):
     pytest.fail(message)
 
 class RaisesContext(object):
-    def __init__(self, expected_exception, message):
+    def __init__(self, expected_exception, message, match_info):
         self.expected_exception = expected_exception
         self.message = message
+        self.match_info = match_info
         self.excinfo = None
 
     def __enter__(self):
@@ -1243,6 +1254,8 @@ def __exit__(self, *tp):
                 exc_type, value, traceback = tp
                 tp = exc_type, exc_type(value), traceback
         self.excinfo.__init__(tp)
+        if self.match_info and not self.match_info.lower() in str(self.excinfo).lower():
+            pytest.fail(self.message)
         suppress_exception = issubclass(self.excinfo.type, self.expected_exception)
         if sys.version_info[0] == 2 and suppress_exception:
             sys.exc_clear()

testing/python/raises.py

@@ -118,3 +118,16 @@ def __call__(self):
         for o in gc.get_objects():
             assert type(o) is not T
 
+
+    def test_raises_match_info(self):
+        msg = "with base 10"
+        with pytest.raises(ValueError, match_info=msg):
+            int('asdf')
+
+        try:
+            with pytest.raises(ValueError, match_info=msg):
+                int('asdf', base=16)
+        except pytest.raises.Exception as e:
+            assert e.msg == "DID NOT RAISE {0} with text '{1}'".format(repr(ValueError), msg)
+        else:
+            assert False, "Expected pytest.raises.Exception"