Add more tests on LazyStream class

contains enough tests to make full coverage on LazyStream class

tests/multipartparser/tests.py

@@ -0,0 +1,90 @@
+import unittest
+from django.core.exceptions import SuspiciousMultipartForm
+from django.http import multipartparser
+
+
+class LazyStreamTests(unittest.TestCase):
+    def test_lazy_stream_iteration_scenario(self):
+        stream = multipartparser.LazyStream(iter([b'1', b'2', b'3']))
+        item = next(stream)
+        self.assertEqual(item, b'1')
+        item = next(stream)
+        self.assertEqual(item, b'2')
+        item = next(stream)
+        self.assertEqual(item, b'3')
+        with self.assertRaises(StopIteration):
+            next(stream)
+
+    def test_lazy_stream_unget_scenario(self):
+        stream = multipartparser.LazyStream(iter([b'1', b'2', b'3']))
+        item = next(stream)
+        self.assertEqual(item, b'1')
+
+        stream.unget(b'4')
+
+        item = next(stream)
+        self.assertEqual(item, b'4')
+        item = next(stream)
+        self.assertEqual(item, b'2')
+        item = next(stream)
+        self.assertEqual(item, b'3')
+        with self.assertRaises(StopIteration):
+            next(stream)
+
+    def test_lazy_stream_full_read_operation_with_ungetting_before(self):
+        stream = multipartparser.LazyStream(iter([b'4', b'5', b'6']))
+        stream.unget(b'123')
+        self.assertEqual(stream.read(), b'123456')
+
+    def test_lazy_stream_partial_read_operation_with_ungetting_before(self):
+        stream = multipartparser.LazyStream(iter([b'4', b'5', b'6']))
+        stream.unget(b'123')
+        self.assertEqual(stream.read(size=2), b'12')
+        self.assertEqual(stream.read(size=2), b'34')
+        self.assertEqual(stream.read(size=2), b'56')
+
+    def test_lazy_stream_read_until_stop_iteration(self):
+
+        stream = multipartparser.LazyStream(iter([b'1', b'2', b'3']))
+        self.assertEqual(stream.read(size=1), b'1')
+        self.assertEqual(stream.read(size=1), b'2')
+        self.assertEqual(stream.read(size=1), b'3')
+        self.assertEqual(stream.read(size=1), b'')
+        self.assertEqual(stream.read(size=1), b'')
+        self.assertEqual(stream.read(size=1), b'')
+        self.assertEqual(stream.read(size=1), b'')
+        self.assertEqual(stream.read(size=1), b'')
+        self.assertEqual(stream.read(size=1), b'')
+
+    def test_lazy_stream_close_stream_and_try_to_read_should_fail(self):
+        stream = multipartparser.LazyStream(iter([b'4', b'5', b'6']))
+        stream.close()
+        with self.assertRaises(Exception):
+            # TypeError: 'list' object is not an iterator
+            stream.read()
+
+    def test_lazy_stream_unget_should_change_tell_result(self):
+        stream = multipartparser.LazyStream(iter([b'4', b'5', b'6']))
+        next(stream)
+        self.assertEqual(stream.tell(), 1)
+        next(stream)
+        self.assertEqual(stream.tell(), 2)
+        stream.unget(b'1')
+        self.assertEqual(stream.tell(), 1)
+        next(stream)
+        self.assertEqual(stream.tell(), 2)
+        stream.unget(b'1')
+        self.assertEqual(stream.tell(), 1)
+        stream.unget(b'2')
+        self.assertEqual(stream.tell(), 0)
+        stream.unget(b'3')
+        self.assertEqual(stream.tell(), -1)
+        stream.unget(b'4')
+        self.assertEqual(stream.tell(), -2)
+
+    def test_lazy_stream_with_a_maliciously_malformed_mime_request(self):
+        stream = multipartparser.LazyStream(iter([]))
+        with self.assertRaises(SuspiciousMultipartForm):
+            while True:
+                stream.unget(b"Hey :D")
+