pytest.warns checks for subclass relationship

rather than class equality. This makes it more similar to
pytest.raises.

CHANGELOG.rst

@@ -8,7 +8,8 @@ New Features
 * Added an ini option ``doctest_encoding`` to specify which encoding to use for doctest files.
   Thanks `@wheerd`_ for the PR (`#2101`_).
 
-*
+* ``pytest.warns`` now checks for subclass relationship rather than
+  class equality. Thanks `@lesteve`_ for the PR (`#2163`_)
 
 
 Changes
@@ -40,13 +41,14 @@ Changes
 .. _@fushi: https://github.com/fushi
 .. _@mattduck: https://github.com/mattduck
 .. _@wheerd: https://github.com/wheerd
+.. _@lesteve: https://github.com/lesteve
 
 .. _#1512: https://github.com/pytest-dev/pytest/issues/1512
 .. _#1874: https://github.com/pytest-dev/pytest/pull/1874
 .. _#1952: https://github.com/pytest-dev/pytest/pull/1952
 .. _#2013: https://github.com/pytest-dev/pytest/issues/2013
 .. _#2101: https://github.com/pytest-dev/pytest/pull/2101
-
+.. _#2164: https://github.com/pytest-dev/pytest/pull/2164
 
 3.0.5.dev0
 ==========

_pytest/recwarn.py

@@ -216,6 +216,7 @@ def __exit__(self, *exc_info):
         # 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):
+                if not any(issubclass(r.category, exp_warning) for
+                           exp_warning in self.expected_warning for r in self):
                     __tracebackhide__ = True
                     pytest.fail("DID NOT WARN")

testing/test_recwarn.py

@@ -215,6 +215,16 @@ def test_record_only(self):
         assert str(record[0].message) == "user"
         assert str(record[1].message) == "runtime"
 
+    def test_record_by_subclass(self):
+        with pytest.warns(Warning) as record:
+            warnings.warn("user", UserWarning)
+            warnings.warn("runtime", RuntimeWarning)
+
+        assert len(record) == 2
+        assert str(record[0].message) == "user"
+        assert str(record[1].message) == "runtime"
+
+
     def test_double_test(self, testdir):
         """If a test is run again, the warning should still be raised"""
         testdir.makepyfile('''