diff --git a/pydu/misc.py b/pydu/misc.py
index 445bfa9..e8a377b 100644
--- a/pydu/misc.py
+++ b/pydu/misc.py
@@ -148,7 +148,6 @@ def memoize_when_activated(fun):
     return wrapper
 
 
-# todo doc test
 # https://github.com/requests/requests/blob/master/requests/utils.py
 def super_len(o):
     total_length = None
diff --git a/tests/test_misc.py b/tests/test_misc.py
index e9bd91e..c66d63b 100644
--- a/tests/test_misc.py
+++ b/tests/test_misc.py
@@ -2,7 +2,8 @@ import sys
 import time
 import pytest
 from pydu import WINDOWS
-from pydu.misc import trace, unix_timeout, TimeoutError, memoize, memoize_when_activated
+from pydu.misc import trace, unix_timeout, TimeoutError, memoize, memoize_when_activated, super_len
+
 try:
     from cStringIO import StringIO  # py2
 except ImportError:
@@ -66,14 +67,14 @@ def test_memoize():
     # with args
     for x in range(2):
         ret = foo(1)
-        expected = ((1, ), {})
+        expected = ((1,), {})
         assert ret == expected
         assert len(calls) == 2
 
     # with args + kwargs
     for x in range(2):
         ret = foo(1, bar=2)
-        expected = ((1, ), {'bar': 2})
+        expected = ((1,), {'bar': 2})
         assert ret == expected
         assert len(calls) == 3
 
@@ -90,7 +91,6 @@ def test_memoize():
 
 def test_memoize_when_activated():
     class Foo:
-
         @memoize_when_activated
         def foo(self):
             calls.append(None)
@@ -113,4 +113,90 @@ def test_memoize_when_activated():
     f.foo.cache_deactivate()
     f.foo()
     f.foo()
-    assert len(calls) == 2
\ No newline at end of file
+    assert len(calls) == 2
+
+
+class TestSuperLen:
+    @pytest.mark.parametrize(
+        'stream, value', (
+            (StringIO, 'Test'),
+        ))
+    def test_io_streams(self, stream, value):
+        """Ensures that we properly deal with different kinds of IO streams."""
+        assert super_len(stream()) == 0
+        assert super_len(stream(value)) == 4
+
+    def test_super_len_correctly_calculates_len_of_partially_read_file(self):
+        """Ensure that we handle partially consumed file like objects."""
+        s = StringIO()
+        s.write('foobarbogus')
+        assert super_len(s) == 0
+
+    @pytest.mark.parametrize('error', [IOError, OSError])
+    def test_super_len_handles_files_raising_weird_errors_in_tell(self, error):
+        """If tell() raises errors, assume the cursor is at position zero."""
+
+        class BoomFile(object):
+            def __len__(self):
+                return 5
+
+            def tell(self):
+                raise error()
+
+        assert super_len(BoomFile()) == 0
+
+    @pytest.mark.parametrize('error', [IOError, OSError])
+    def test_super_len_tell_ioerror(self, error):
+        """Ensure that if tell gives an IOError super_len doesn't fail"""
+
+        class NoLenBoomFile(object):
+            def tell(self):
+                raise error()
+
+            def seek(self, offset, whence):
+                pass
+
+        assert super_len(NoLenBoomFile()) == 0
+
+    def test_string(self):
+        assert super_len('Test') == 4
+
+    @pytest.mark.parametrize(
+        'mode, warnings_num', (
+            ('r', 0),
+            ('rb', 0),
+        ))
+    def test_file(self, tmpdir, mode, warnings_num, recwarn):
+        file_obj = tmpdir.join('test.txt')
+        file_obj.write('Test')
+        with file_obj.open(mode) as fd:
+            assert super_len(fd) == 4
+        assert len(recwarn) == warnings_num
+
+    def test_super_len_with__len__(self):
+        foo = [1, 2, 3, 4]
+        len_foo = super_len(foo)
+        assert len_foo == 4
+
+    def test_super_len_with_no__len__(self):
+        class LenFile(object):
+            def __init__(self):
+                self.len = 5
+
+        assert super_len(LenFile()) == 5
+
+    def test_super_len_with_tell(self):
+        foo = StringIO('12345')
+        assert super_len(foo) == 5
+        foo.read(2)
+        assert super_len(foo) == 3
+
+    def test_super_len_with_fileno(self):
+        with open(__file__, 'rb') as f:
+            length = super_len(f)
+            file_data = f.read()
+        assert length == len(file_data)
+
+    def test_super_len_with_no_matches(self):
+        """Ensure that objects without any length methods default to 0"""
+        assert super_len(object()) == 0