Issue #11747: Fix range formatting in context and unified diffs.

1 files changed, 16 insertions, 0 deletions

diff --git a/Lib/test/test_difflib.py b/Lib/test/test_difflib.py
index a263ee6c73..b08be53dd9 100644
--- a/Lib/test/test_difflib.py
+++ b/Lib/test/test_difflib.py
@@ -236,6 +236,22 @@ class TestOutputFormat(unittest.TestCase):
         cd = difflib.context_diff(*args, lineterm='')
         self.assertEqual(list(cd)[0:2], ["*** Original", "--- Current"])
 
+    def test_range_format(self):
+        # Per the diff spec at http://www.unix.org/single_unix_specification/
+        spec = '''\
+           Each <range> field shall be of the form:
+             %1d", <beginning line number>  if the range contains exactly one line,
+           and:
+            "%1d,%1d", <beginning line number>, <number of lines> otherwise.
+           If a range is empty, its beginning line number shall be the number of
+           the line just before the range, or 0 if the empty range starts the file.
+        '''
+        fmt = difflib._format_range
+        self.assertEqual(fmt(3,3), '3,0')
+        self.assertEqual(fmt(3,4), '4')
+        self.assertEqual(fmt(3,5), '4,2')
+        self.assertEqual(fmt(3,6), '4,3')
+        self.assertEqual(fmt(0,0), '0,0')
 
 def test_main():
     difflib.HtmlDiff._default_prefix = 0