From c5f0b751f48d1c44e74d14e7d89772b825ffa332 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20Est=C3=A8ve?= <loic.esteve@ymail.com>
Date: Tue, 20 Dec 2016 13:36:57 +0100
Subject: [PATCH 1/2] Improve error message when pytest.warns fail

The error message contains the expected type of warnings and the
warnings that were captured. Add tests.
---
 _pytest/recwarn.py      |  5 ++++-
 testing/test_recwarn.py | 41 ++++++++++++++++++++++++++++++++---------
 2 files changed, 36 insertions(+), 10 deletions(-)

diff --git a/_pytest/recwarn.py b/_pytest/recwarn.py
index 87823bfbc..d66f87e72 100644
--- a/_pytest/recwarn.py
+++ b/_pytest/recwarn.py
@@ -223,4 +223,7 @@ class WarningsChecker(WarningsRecorder):
             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")
+                    pytest.fail("DID NOT WARN. No warnings of type {0} was emitted. "
+                                "The list of emitted warnings is: {1}.".format(
+                                    self.expected_warning,
+                                    [each.message for each in self]))
diff --git a/testing/test_recwarn.py b/testing/test_recwarn.py
index 87e5846c2..0f3bf6a14 100644
--- a/testing/test_recwarn.py
+++ b/testing/test_recwarn.py
@@ -1,4 +1,5 @@
 import warnings
+import re
 import py
 import pytest
 from _pytest.recwarn import WarningsRecorder
@@ -114,7 +115,7 @@ class TestDeprecatedCall(object):
         with pytest.raises(pytest.fail.Exception) as ex:
             with pytest.deprecated_call():
                 self.dep(1)
-        assert str(ex.value) == "DID NOT WARN"
+        assert str(ex.value).startswith("DID NOT WARN")
 
     def test_deprecated_call_as_context_manager(self):
         with pytest.deprecated_call():
@@ -185,17 +186,39 @@ class TestWarns(object):
         with pytest.warns(RuntimeWarning):
             warnings.warn("runtime", RuntimeWarning)
 
-        with pytest.raises(pytest.fail.Exception):
-            with pytest.warns(RuntimeWarning):
-                warnings.warn("user", UserWarning)
-
-        with pytest.raises(pytest.fail.Exception):
-            with pytest.warns(UserWarning):
-                warnings.warn("runtime", RuntimeWarning)
-
         with pytest.warns(UserWarning):
             warnings.warn("user", UserWarning)
 
+        with pytest.raises(pytest.fail.Exception) as excinfo:
+            with pytest.warns(RuntimeWarning):
+                warnings.warn("user", UserWarning)
+        excinfo.match(r"DID NOT WARN. No warnings of type \(.+RuntimeWarning.+,\) was emitted. "
+                      r"The list of emitted warnings is: \[UserWarning\('user',\)\].")
+
+        with pytest.raises(pytest.fail.Exception) as excinfo:
+            with pytest.warns(UserWarning):
+                warnings.warn("runtime", RuntimeWarning)
+        excinfo.match(r"DID NOT WARN. No warnings of type \(.+UserWarning.+,\) was emitted. "
+                      r"The list of emitted warnings is: \[RuntimeWarning\('runtime',\)\].")
+
+        with pytest.raises(pytest.fail.Exception) as excinfo:
+            with pytest.warns(UserWarning):
+                pass
+        excinfo.match(r"DID NOT WARN. No warnings of type \(.+UserWarning.+,\) was emitted. "
+                      r"The list of emitted warnings is: \[\].")
+
+        warning_classes = (UserWarning, FutureWarning)
+        with pytest.raises(pytest.fail.Exception) as excinfo:
+            with pytest.warns(warning_classes) as warninfo:
+                warnings.warn("runtime", RuntimeWarning)
+                warnings.warn("import", ImportWarning)
+
+        message_template = ("DID NOT WARN. No warnings of type {0} was emitted. "
+                            "The list of emitted warnings is: {1}.")
+        excinfo.match(re.escape(message_template.format(warning_classes,
+                                                        [each.message for each in warninfo])))
+
+
     def test_record(self):
         with pytest.warns(UserWarning) as record:
             warnings.warn("user", UserWarning)

From bfada968d3d1947523a6cf70f59d44620a9505c9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20Est=C3=A8ve?= <loic.esteve@ymail.com>
Date: Tue, 20 Dec 2016 14:36:10 +0100
Subject: [PATCH 2/2] Update AUTHORS and CHANGELOG.rst

following contribution guidelines
---
 AUTHORS       | 1 +
 CHANGELOG.rst | 7 ++++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/AUTHORS b/AUTHORS
index 8c7cb19ce..8c6fa1b5d 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -82,6 +82,7 @@ Katarzyna Jachim
 Kevin Cox
 Lee Kamentsky
 Lev Maximov
+Loic Esteve
 Lukas Bednar
 Luke Murphy
 Maciek Fijalkowski
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 707253958..847d27c51 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -5,12 +5,17 @@
 
 *
 
-*
+* Improve error message when pytest.warns fails (`#2150`_). The type(s) of the
+  expected warnings and the list of caught warnings is added to the
+  error message. Thanks `@lesteve`_ for the PR.
 
 *
 
 *
 
+.. _@lesteve: https://github.com/lesteve
+
+.. _#2150: https://github.com/pytest-dev/pytest/issues/2150
 
 
 3.0.5 (2016-12-05)