diff -r 629852f6d186 Lib/test/test_imghdr.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/test/test_imghdr.py	Mon Dec 16 09:53:40 2013 +0200
@@ -0,0 +1,64 @@
+import unittest
+from test.support import TESTFN, unlink
+import imghdr
+
+FORMATS = {
+    'png': (b'\211PNG\r\n\032\n', ),
+    'rgb': (b'\001\332', ),
+    'rast': (b'\x59\xA6\x6A\x95', ),
+    'xbm': (b'#define ', ),
+    'bmp': (b'BM', ),
+    'jpeg': (b'000000JFIF', b'000000Exif'),
+    'gif': (b'GIF87a', b'GIF89a'),
+    'tiff': (b'MM', b'II'),
+    'pbm': (b'P1\t', b'P1\n', b'P1\r',
+            b'P4\t', b'P4\n', b'P4\r'),
+    'pgm': (b'P2\t', b'P2\n', b'P2\r',
+            b'P5\t', b'P5\n', b'P5\r'),
+    'ppm': (b'P3\t', b'P6\n', b'P6\r',
+            b'P6\t', b'P6\n', b'P6\r')
+}
+
+
+class TestImghdr(unittest.TestCase):
+    def tearDown(self):
+        unlink(TESTFN)
+
+    def test_formats_without_file(self):
+        for format, parts in FORMATS.items():
+            for part in parts:
+                self.assertEqual(imghdr.what(None, part),
+                                 format)
+
+    def test_format_with_files(self):
+        for format, parts in FORMATS.items():
+            for part in parts:
+                with open(TESTFN, 'wb') as stream:
+                    stream.write(part)
+                with open(TESTFN, 'rb') as stream:
+                    self.assertEqual(imghdr.what(stream),
+                                     format)
+                self.assertEqual(imghdr.what(TESTFN),
+                                 format)
+
+    def test_register_test(self):
+        def test_jumbo(h, file):
+            if h.startswith(b'eggs'):
+                return 'ham'
+        imghdr.tests.append(test_jumbo)
+        self.addCleanup(imghdr.tests.pop)
+
+        self.assertEqual(imghdr.what(None, b'eggs'), 'ham')
+
+    def test_invalid_headers(self):
+        for header in (b'\211PN\r\n',
+                       b'\001\331',
+                       b'\x59\xA6',
+                       b'cutecat',
+                       b'000000JFI',
+                       b'GIF80'):
+            self.assertIsNone(imghdr.what(None, header))
+
+
+if __name__ == '__main__':
+    unittest.main()
diff -r 629852f6d186 Lib/test/test_sundry.py
--- a/Lib/test/test_sundry.py	Sun Dec 15 21:49:17 2013 +0100
+++ b/Lib/test/test_sundry.py	Mon Dec 16 09:53:40 2013 +0200
@@ -6,7 +6,7 @@
 
 class TestUntestedModules(unittest.TestCase):
     def test_untested_modules_can_be_imported(self):
-        untested = ('bdb', 'encodings', 'formatter', 'imghdr',
+        untested = ('bdb', 'encodings', 'formatter',
                     'nturl2path', 'tabnanny')
         with support.check_warnings(quiet=True):
             for name in untested: