issue 1553: Include terminal newlines in diffs

Author: tomviner

CHANGELOG.rst

@@ -17,14 +17,20 @@
   is specified on the command line together with the ``--pyargs``
   option.  Thanks to `@taschini`_ for the PR (`#1597`_).
 
+* Create correct diff for strings ending with newlines. Fixes (`#1553`_).
+  Thanks `@Vogtinator`_ for reporting. Thanks to `@RedBeardCode`_ and
+  `@tomviner`_ for PR.
+
 *
 
 .. _#1580: https://github.com/pytest-dev/pytest/pull/1580
 .. _#1605: https://github.com/pytest-dev/pytest/issues/1605
 .. _#1597: https://github.com/pytest-dev/pytest/pull/1597
+.. _#1553: https://github.com/pytest-dev/pytest/issues/1553
 
 .. _@graingert: https://github.com/graingert
 .. _@taschini: https://github.com/taschini
+.. _@Vogtinator: https://github.com/Vogtinator
 
 
 2.9.2

_pytest/assertion/util.py

@@ -225,9 +225,11 @@ def _diff_text(left, right, verbose=False):
                                   'characters in diff, use -v to show') % i]
                 left = left[:-i]
                 right = right[:-i]
+    # We set splitlines' keepends=True, which can only be passed as a
+    # positional argument
     explanation += [line.strip('\n')
-                    for line in ndiff(left.splitlines(),
-                                      right.splitlines())]
+                    for line in ndiff(left.splitlines(True),
+                                      right.splitlines(True))]
     return explanation
 
 

testing/test_assertion.py

@@ -428,7 +428,7 @@ def test_long():
         "*- 3",
         "*- 5",
         "*- 7",
-        "*truncated (191 more lines)*use*-vv*",
+        "*truncated (193 more lines)*use*-vv*",
     ])
 
 
@@ -626,3 +626,17 @@ def __hash__(self):
         + repr(3)
     """).strip()
     assert '\n'.join(expl) == dedent
+
+def test_diff_newline_at_end(monkeypatch, testdir):
+    testdir.makepyfile(r"""
+        def test_diff():
+            assert 'asdf' == 'asdf\n'
+    """)
+
+    result = testdir.runpytest()
+    result.stdout.fnmatch_lines(r"""
+        *assert 'asdf' == 'asdf\n'
+        *  - asdf
+        *  + asdf
+        *  ?     +
+    """)