Fix UnicodeEncodeError when string comparison with unicode has failed.

AUTHORS

@@ -5,6 +5,7 @@ Contributors include::
 
 Abdeali JK
 Abhijeet Kasurde
+Ahn Ki-Wook
 Alexei Kozlenok
 Anatoly Bubenkoff
 Andreas Zeidler

CHANGELOG.rst

@@ -9,11 +9,16 @@
 * Add ``buffer`` attribute to stdin stub class ``pytest.capture.DontReadFromInput``
   Thanks `@joguSD`_ for the PR.
 
+* Fix ``UnicodeEncodeError`` when string comparison with unicode has failed. (`#1864`_)
+  Thanks `@AiOO`_ for the PR
+
 *
 
 .. _@joguSD: https://github.com/joguSD
+.. _@AiOO: https://github.com/AiOO
 
 .. _#1857: https://github.com/pytest-dev/pytest/issues/1857
+.. _#1864: https://github.com/pytest-dev/pytest/issues/1864
 
 
 3.0.1

_pytest/_code/code.py

@@ -354,7 +354,7 @@ def __init__(self, tup=None, exprinfo=None):
             if exprinfo is None and isinstance(tup[1], AssertionError):
                 exprinfo = getattr(tup[1], 'msg', None)
                 if exprinfo is None:
-                    exprinfo = str(tup[1])
+                    exprinfo = py._builtin._totext(tup[1])
                 if exprinfo and exprinfo.startswith('assert '):
                     self._striptext = 'AssertionError: '
         self._excinfo = tup

testing/test_assertion.py

@@ -816,3 +816,12 @@ def test_tuple():
     result = testdir.runpytest('-rw')
     output = '\n'.join(result.stdout.lines)
     assert 'WR1' not in output
+
+def test_assert_with_unicode(monkeypatch, testdir):
+    testdir.makepyfile(u"""
+        # -*- coding: utf-8 -*-
+        def test_unicode():
+            assert u'유니코드' == u'Unicode'
+    """)
+    result = testdir.runpytest()
+    result.stdout.fnmatch_lines(['*AssertionError*'])