diff --git a/tests/test_construct.py b/tests/test_construct.py
index ad409b1..f1bee5a 100644
--- a/tests/test_construct.py
+++ b/tests/test_construct.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 
 import unittest
-from pySim.construct import GreedyInteger
+from pySim.construct import *
 
 tests = [
         ( b'\x80', 0x80 ),
@@ -21,6 +21,17 @@
             self.assertEqual(t[0], gi.build(t[1]))
         pass
 
+class TestUtils(unittest.TestCase):
+    def test_filter_dict(self):
+        inp = {'foo': 0xf00, '_bar' : 0xba5, 'baz': 0xba2 }
+        out = {'foo': 0xf00, 'baz': 0xba2 }
+        self.assertEqual(filter_dict(inp), out)
+
+    def test_filter_dict_nested(self):
+        inp = {'foo': 0xf00, 'nest': {'_bar' : 0xba5}, 'baz': 0xba2 }
+        out = {'foo': 0xf00, 'nest': {}, 'baz': 0xba2 }
+        self.assertEqual(filter_dict(inp), out)
+
 
 if __name__ == "__main__":
 	unittest.main()
diff --git a/tests/test_tlv.py b/tests/test_tlv.py
new file mode 100644
index 0000000..1e5000d
--- /dev/null
+++ b/tests/test_tlv.py
@@ -0,0 +1,120 @@
+#!/usr/bin/env python3
+
+# (C) 2022 by Harald Welte <laforge@osmocom.org>
+# All Rights Reserved
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import unittest
+from pySim.tlv import *
+
+class TestUtils(unittest.TestCase):
+    def test_camel_to_snake(self):
+        cases = [
+            ('CamelCase', 'camel_case'),
+            ('CamelCaseUPPER', 'camel_case_upper'),
+            ('Camel_CASE_underSCORE', 'camel_case_under_score'),
+        ]
+        for c in cases:
+            self.assertEqual(camel_to_snake(c[0]), c[1])
+
+    def test_flatten_dict_lists(self):
+        inp = [
+                { 'first': 1 },
+                { 'second': 2 },
+                { 'third': 3 },
+                ]
+        out = { 'first': 1, 'second':2, 'third': 3}
+        self.assertEqual(flatten_dict_lists(inp), out)
+
+    def test_flatten_dict_lists_nodict(self):
+        inp = [
+                { 'first': 1 },
+                { 'second': 2 },
+                { 'third': 3 },
+                4,
+                ]
+        self.assertEqual(flatten_dict_lists(inp), inp)
+
+    def test_flatten_dict_lists_nested(self):
+        inp = {'top': [
+                { 'first': 1 },
+                { 'second': 2 },
+                { 'third': 3 },
+                ] }
+        out = {'top': { 'first': 1, 'second':2, 'third': 3 } }
+        self.assertEqual(flatten_dict_lists(inp), out)
+
+class TestTranscodable(unittest.TestCase):
+    class XC_constr_class(Transcodable):
+        _construct = Int8ub
+        def __init__(self):
+            super().__init__();
+
+    def test_XC_constr_class(self):
+        """Transcodable derived class with _construct class variable"""
+        xc = TestTranscodable.XC_constr_class()
+        self.assertEqual(xc.from_bytes(b'\x23'), 35)
+        self.assertEqual(xc.to_bytes(), b'\x23')
+
+    class XC_constr_instance(Transcodable):
+        def __init__(self):
+            super().__init__();
+            self._construct = Int8ub
+
+    def test_XC_constr_instance(self):
+        """Transcodable derived class with _construct instance variable"""
+        xc = TestTranscodable.XC_constr_instance()
+        self.assertEqual(xc.from_bytes(b'\x23'), 35)
+        self.assertEqual(xc.to_bytes(), b'\x23')
+
+    class XC_method_instance(Transcodable):
+        def __init__(self):
+            super().__init__();
+        def _from_bytes(self, do):
+            return ('decoded', do)
+        def _to_bytes(self):
+            return self.decoded[1]
+
+    def test_XC_method_instance(self):
+        """Transcodable derived class with _{from,to}_bytes() methods"""
+        xc = TestTranscodable.XC_method_instance()
+        self.assertEqual(xc.to_bytes(), b'')
+        self.assertEqual(xc.from_bytes(b''), None)
+        self.assertEqual(xc.from_bytes(b'\x23'), ('decoded', b'\x23'))
+        self.assertEqual(xc.to_bytes(), b'\x23')
+
+class TestIE(unittest.TestCase):
+    class MyIE(IE, tag=0x23, desc='My IE description'):
+        _construct = Int8ub
+        def to_ie(self):
+            return self.to_bytes()
+
+    def test_IE_empty(self):
+        ie = TestIE.MyIE()
+        self.assertEqual(ie.to_dict(), {'my_ie': None})
+        self.assertEqual(repr(ie), 'MyIE(None)')
+        self.assertEqual(ie.is_constructed(), False)
+
+    def test_IE_from_bytes(self):
+        ie = TestIE.MyIE()
+        ie.from_bytes(b'\x42')
+        self.assertEqual(ie.to_dict(), {'my_ie': 66})
+        self.assertEqual(repr(ie), 'MyIE(66)')
+        self.assertEqual(ie.is_constructed(), False)
+        self.assertEqual(ie.to_bytes(), b'\x42')
+        self.assertEqual(ie.to_ie(), b'\x42')
+
+if __name__ == "__main__":
+	unittest.main()