Add new tests for bytes and bytearray constructors. (GH-9843)

Covered all special cases: bytes, tuple, list, differend
kinds of iterables and iterators.
(cherry picked from commit 1a997eb291)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Lib/test/test_bytes.py

@@ -69,11 +69,49 @@ class BaseBytesTest:
         self.assertRaises(IndexError, lambda: b[-sys.maxsize-2])
         self.assertRaises(IndexError, lambda: b[-10**100])
 
-    def test_from_list(self):
-        ints = list(range(256))
-        b = self.type2test(i for i in ints)
+    def test_from_iterable(self):
+        b = self.type2test(range(256))
         self.assertEqual(len(b), 256)
-        self.assertEqual(list(b), ints)
+        self.assertEqual(list(b), list(range(256)))
+
+        # Non-sequence iterable.
+        b = self.type2test({42})
+        self.assertEqual(b, b"*")
+        b = self.type2test({43, 45})
+        self.assertIn(tuple(b), {(43, 45), (45, 43)})
+
+        # Iterator that has a __length_hint__.
+        b = self.type2test(iter(range(256)))
+        self.assertEqual(len(b), 256)
+        self.assertEqual(list(b), list(range(256)))
+
+        # Iterator that doesn't have a __length_hint__.
+        b = self.type2test(i for i in range(256) if i % 2)
+        self.assertEqual(len(b), 128)
+        self.assertEqual(list(b), list(range(256))[1::2])
+
+        # Sequence without __iter__.
+        class S:
+            def __getitem__(self, i):
+                return (1, 2, 3)[i]
+        b = self.type2test(S())
+        self.assertEqual(b, b"\x01\x02\x03")
+
+    def test_from_tuple(self):
+        # There is a special case for tuples.
+        b = self.type2test(tuple(range(256)))
+        self.assertEqual(len(b), 256)
+        self.assertEqual(list(b), list(range(256)))
+        b = self.type2test((1, 2, 3))
+        self.assertEqual(b, b"\x01\x02\x03")
+
+    def test_from_list(self):
+        # There is a special case for lists.
+        b = self.type2test(list(range(256)))
+        self.assertEqual(len(b), 256)
+        self.assertEqual(list(b), list(range(256)))
+        b = self.type2test([1, 2, 3])
+        self.assertEqual(b, b"\x01\x02\x03")
 
     def test_from_index(self):
         b = self.type2test([Indexable(), Indexable(1), Indexable(254),
@@ -85,6 +123,8 @@ class BaseBytesTest:
     def test_from_buffer(self):
         a = self.type2test(array.array('B', [1, 2, 3]))
         self.assertEqual(a, b"\x01\x02\x03")
+        a = self.type2test(b"\x01\x02\x03")
+        self.assertEqual(a, b"\x01\x02\x03")
 
         # http://bugs.python.org/issue29159
         # Fallback when __index__ raises exception other than OverflowError