diff --git a/test/mitmproxy/test_tnetstring.py b/test/mitmproxy/test_tnetstring.py
new file mode 100644
index 000000000..0b16437be
--- /dev/null
+++ b/test/mitmproxy/test_tnetstring.py
@@ -0,0 +1,141 @@
+import unittest
+import random
+import math
+import io
+import struct
+
+from mitmproxy import tnetstring
+
+MAXINT = 2 ** (struct.Struct('i').size * 8 - 1) - 1
+
+FORMAT_EXAMPLES = {
+    b'0:}': {},
+    b'0:]': [],
+    b'51:5:hello,39:11:12345678901#4:this,4:true!0:~4:\x00\x00\x00\x00,]}':
+    {b'hello': [12345678901, b'this', True, None, b'\x00\x00\x00\x00']},
+    b'5:12345#': 12345,
+    b'12:this is cool,': b'this is cool',
+    b'0:,': b'',
+    b'0:~': None,
+    b'4:true!': True,
+    b'5:false!': False,
+    b'10:\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00,': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00',
+    b'24:5:12345#5:67890#5:xxxxx,]': [12345, 67890, b'xxxxx'],
+    b'18:3:0.1^3:0.2^3:0.3^]': [0.1, 0.2, 0.3],
+    b'243:238:233:228:223:218:213:208:203:198:193:188:183:178:173:168:163:158:153:148:143:138:133:128:123:118:113:108:103:99:95:91:87:83:79:75:71:67:63:59:55:51:47:43:39:35:31:27:23:19:15:11:hello-there,]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]': [[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[b'hello-there']]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]  # noqa
+}
+
+
+def get_random_object(random=random, depth=0):
+    """Generate a random serializable object."""
+    #  The probability of generating a scalar value increases as the depth increase.
+    #  This ensures that we bottom out eventually.
+    if random.randint(depth, 10) <= 4:
+        what = random.randint(0, 1)
+        if what == 0:
+            n = random.randint(0, 10)
+            l = []
+            for _ in range(n):
+                l.append(get_random_object(random, depth + 1))
+            return l
+        if what == 1:
+            n = random.randint(0, 10)
+            d = {}
+            for _ in range(n):
+                n = random.randint(0, 100)
+                k = bytes([random.randint(32, 126) for _ in range(n)])
+                d[k] = get_random_object(random, depth + 1)
+            return d
+    else:
+        what = random.randint(0, 4)
+        if what == 0:
+            return None
+        if what == 1:
+            return True
+        if what == 2:
+            return False
+        if what == 3:
+            if random.randint(0, 1) == 0:
+                return random.randint(0, MAXINT)
+            else:
+                return -1 * random.randint(0, MAXINT)
+        n = random.randint(0, 100)
+        return bytes([random.randint(32, 126) for _ in range(n)])
+
+
+class Test_Format(unittest.TestCase):
+
+    def test_roundtrip_format_examples(self):
+        for data, expect in FORMAT_EXAMPLES.items():
+            self.assertEqual(expect, tnetstring.loads(data))
+            self.assertEqual(
+                expect, tnetstring.loads(tnetstring.dumps(expect)))
+            self.assertEqual((expect, b''), tnetstring.pop(data))
+
+    def test_roundtrip_format_random(self):
+        for _ in range(500):
+            v = get_random_object()
+            self.assertEqual(v, tnetstring.loads(tnetstring.dumps(v)))
+            self.assertEqual((v, b""), tnetstring.pop(tnetstring.dumps(v)))
+
+    def test_unicode_handling(self):
+        with self.assertRaises(ValueError):
+            tnetstring.dumps(u"hello")
+        self.assertEqual(tnetstring.dumps(u"hello".encode()), b"5:hello,")
+        self.assertEqual(type(tnetstring.loads(b"5:hello,")), bytes)
+
+    def test_roundtrip_format_unicode(self):
+        for _ in range(500):
+            v = get_random_object()
+            self.assertEqual(v, tnetstring.loads(tnetstring.dumps(v)))
+            self.assertEqual((v, b''), tnetstring.pop(tnetstring.dumps(v)))
+
+    def test_roundtrip_big_integer(self):
+        i1 = math.factorial(30000)
+        s = tnetstring.dumps(i1)
+        i2 = tnetstring.loads(s)
+        self.assertEqual(i1, i2)
+
+
+class Test_FileLoading(unittest.TestCase):
+
+    def test_roundtrip_file_examples(self):
+        for data, expect in FORMAT_EXAMPLES.items():
+            s = io.BytesIO()
+            s.write(data)
+            s.write(b'OK')
+            s.seek(0)
+            self.assertEqual(expect, tnetstring.load(s))
+            self.assertEqual(b'OK', s.read())
+            s = io.BytesIO()
+            tnetstring.dump(expect, s)
+            s.write(b'OK')
+            s.seek(0)
+            self.assertEqual(expect, tnetstring.load(s))
+            self.assertEqual(b'OK', s.read())
+
+    def test_roundtrip_file_random(self):
+        for _ in range(500):
+            v = get_random_object()
+            s = io.BytesIO()
+            tnetstring.dump(v, s)
+            s.write(b'OK')
+            s.seek(0)
+            self.assertEqual(v, tnetstring.load(s))
+            self.assertEqual(b'OK', s.read())
+
+    def test_error_on_absurd_lengths(self):
+        s = io.BytesIO()
+        s.write(b'1000000000:pwned!,')
+        s.seek(0)
+        with self.assertRaises(ValueError):
+            tnetstring.load(s)
+        self.assertEqual(s.read(1), b':')
+
+
+def suite():
+    loader = unittest.TestLoader()
+    suite = unittest.TestSuite()
+    suite.addTest(loader.loadTestsFromTestCase(Test_Format))
+    suite.addTest(loader.loadTestsFromTestCase(Test_FileLoading))
+    return suite