[3.13] gh-138669: Increase test coverage for difflib (GH-138670) (#138818)

gh-138669: Increase test coverage for difflib (GH-138670)
(cherry picked from commit 44991619ba04a98c5878ee5bbc38d2e47cbd22c7)

Co-authored-by: Jan-Eric Nitschke <47750513+JanEricNitschke@users.noreply.github.com>

diff --git a/Lib/test/test_difflib.py b/Lib/test/test_difflib.py
index 6afd90af8442add79afcbccde5fc7e19a6963cb2..943d7a659b1e1b6a8ba444e0bb7ca249557bf632 100644 (file)
--- a/Lib/test/test_difflib.py
+++ b/Lib/test/test_difflib.py
@@ -29,6 +29,16 @@ class TestWithAscii(unittest.TestCase):
                 ('delete', 40, 41, 40, 40),
                 ('equal', 41, 81, 40, 80)])
 
+    def test_opcode_caching(self):
+        sm = difflib.SequenceMatcher(None, 'b' * 100, 'a' + 'b' * 100)
+        opcode = sm.get_opcodes()
+        self.assertEqual(opcode,
+            [   ('insert', 0, 0, 0, 1),
+                ('equal', 0, 100, 1, 101)])
+        # Implementation detail: opcodes are cached;
+        # `get_opcodes()` returns the same object
+        self.assertIs(opcode, sm.get_opcodes())
+
     def test_bjunk(self):
         sm = difflib.SequenceMatcher(isjunk=lambda x: x == ' ',
                 a='a' * 40 + 'b' * 40, b='a' * 44 + 'b' * 40)
@@ -273,6 +283,15 @@ class TestSFpatches(unittest.TestCase):
         self.assertIn('ımplıcıt', output)
 
 
+    def test_one_insert(self):
+        m = difflib.Differ().compare('b' * 2, 'a' + 'b' * 2)
+        self.assertEqual(list(m), ['+ a', '  b', '  b'])
+
+    def test_one_delete(self):
+        m = difflib.Differ().compare('a' + 'b' * 2, 'b' * 2)
+        self.assertEqual(list(m), ['- a', '  b', '  b'])
+
+
 class TestOutputFormat(unittest.TestCase):
     def test_tab_delimiter(self):
         args = ['one', 'two', 'Original', 'Current',
@@ -547,6 +566,26 @@ class TestFindLongest(unittest.TestCase):
         self.assertFalse(self.longer_match_exists(a, b, match.size))
 
 
+class TestCloseMatches(unittest.TestCase):
+    # Happy paths are tested in the doctests of `difflib.get_close_matches`.
+
+    def test_invalid_inputs(self):
+        self.assertRaises(ValueError, difflib.get_close_matches, "spam", ['egg'], n=0)
+        self.assertRaises(ValueError, difflib.get_close_matches, "spam", ['egg'], n=-1)
+        self.assertRaises(ValueError, difflib.get_close_matches, "spam", ['egg'], cutoff=1.1)
+        self.assertRaises(ValueError, difflib.get_close_matches, "spam", ['egg'], cutoff=-0.1)
+
+
+class TestRestore(unittest.TestCase):
+    # Happy paths are tested in the doctests of `difflib.restore`.
+
+    def test_invalid_input(self):
+        with self.assertRaises(ValueError):
+            ''.join(difflib.restore([], 0))
+        with self.assertRaises(ValueError):
+            ''.join(difflib.restore([], 3))
+
+
 def setUpModule():
     difflib.HtmlDiff._default_prefix = 0