Add tests for the writelines() method of file objects.

Original patch by Felipe Cruz.

Lib/test/test_fileio.py

@@ -9,6 +9,7 @@ from weakref import proxy
 from functools import wraps
 
 from test.support import TESTFN, check_warnings, run_unittest, make_bad_fd
+from collections import UserList
 
 from _io import FileIO as _FileIO
 
@@ -67,6 +68,27 @@ class AutoFileTests(unittest.TestCase):
         n = self.f.readinto(a)
         self.assertEqual(array('b', [1, 2]), a[:n])
 
+    def testWritelinesList(self):
+        l = [b'123', b'456']
+        self.f.writelines(l)
+        self.f.close()
+        self.f = _FileIO(TESTFN, 'rb')
+        buf = self.f.read()
+        self.assertEqual(buf, b'123456')
+
+    def testWritelinesUserList(self):
+        l = UserList([b'123', b'456'])
+        self.f.writelines(l)
+        self.f.close()
+        self.f = _FileIO(TESTFN, 'rb')
+        buf = self.f.read()
+        self.assertEqual(buf, b'123456')
+
+    def testWritelinesError(self):
+        self.assertRaises(TypeError, self.f.writelines, [1, 2, 3])
+        self.assertRaises(TypeError, self.f.writelines, None)
+        self.assertRaises(TypeError, self.f.writelines, "abc")
+
     def test_none_args(self):
         self.f.write(b"hi\nbye\nabc")
         self.f.close()

Lib/test/test_io.py

@@ -32,7 +32,7 @@ import errno
 import warnings
 import pickle
 from itertools import cycle, count
-from collections import deque
+from collections import deque, UserList
 from test import support
 
 import codecs
@@ -1177,6 +1177,29 @@ class BufferedWriterTest(unittest.TestCase, CommonBufferedTests):
         bufio.flush()
         self.assertEqual(b"abc", writer._write_stack[0])
 
+    def test_writelines(self):
+        l = [b'ab', b'cd', b'ef']
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        bufio.writelines(l)
+        bufio.flush()
+        self.assertEqual(b''.join(writer._write_stack), b'abcdef')
+
+    def test_writelines_userlist(self):
+        l = UserList([b'ab', b'cd', b'ef'])
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        bufio.writelines(l)
+        bufio.flush()
+        self.assertEqual(b''.join(writer._write_stack), b'abcdef')
+
+    def test_writelines_error(self):
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        self.assertRaises(TypeError, bufio.writelines, [1, 2, 3])
+        self.assertRaises(TypeError, bufio.writelines, None)
+        self.assertRaises(TypeError, bufio.writelines, 'abc')
+
     def test_destructor(self):
         writer = self.MockRawIO()
         bufio = self.tp(writer, 8)