diff --git a/tests/test_primitive_data/test_octet_string.py b/tests/test_primitive_data/test_octet_string.py
index e69de29..7ebe71f 100644
--- a/tests/test_primitive_data/test_octet_string.py
+++ b/tests/test_primitive_data/test_octet_string.py
@@ -0,0 +1,126 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+"""
+Test Primitive Data Octet String
+--------------------------------
+"""
+
+import unittest
+import struct
+
+from bacpypes.debugging import bacpypes_debugging, ModuleLogger, xtob
+from bacpypes.primitivedata import OctetString, Tag
+
+# some debugging
+_debug = 0
+_log = ModuleLogger(globals())
+
+
+@bacpypes_debugging
+def octet_string_tag(x):
+    """Convert a hex string to an octet_string application tag."""
+    if _debug: octet_string_tag._debug("octet_string_tag %r", x)
+
+    b = xtob(x)
+    tag = Tag(Tag.applicationTagClass, Tag.octetStringAppTag, len(b), b)
+    if _debug: octet_string_endec._debug("    - tag: %r", tag)
+
+    return tag
+
+@bacpypes_debugging
+def octet_string_encode(obj):
+    """Encode an OctetString object into a tag."""
+    if _debug: octet_string_encode._debug("octet_string_encode %r", obj)
+
+    tag = Tag()
+    obj.encode(tag)
+    if _debug: octet_string_endec._debug("    - tag: %r", tag)
+
+    return tag
+
+
+@bacpypes_debugging
+def octet_string_decode(tag):
+    """Decode an octet_string application tag into an octet string."""
+    if _debug: octet_string_decode._debug("octet_string_decode %r", tag)
+
+    obj = OctetString(tag)
+    if _debug: octet_string_decode._debug("    - obj: %r", obj)
+
+    return obj
+
+
+@bacpypes_debugging
+def octet_string_endec(x):
+    """Pass the value to OctetString, construct a tag from the hex string,
+    and compare results of encode and decoding each other."""
+    if _debug: octet_string_endec._debug("octet_string_endec %r", x)
+
+    tag = octet_string_tag(x)
+    if _debug: octet_string_endec._debug("    - tag: %r, %r", tag, tag.tagData)
+
+    obj = OctetString(xtob(x))
+    if _debug: octet_string_endec._debug("    - obj: %r, %r", obj, obj.value)
+
+    assert octet_string_encode(obj) == tag
+    assert octet_string_decode(tag) == obj
+
+
+@bacpypes_debugging
+class TestOctetString(unittest.TestCase):
+
+    def test_octet_string(self):
+        if _debug: TestOctetString._debug("test_octet_string")
+
+        obj = OctetString()
+        assert obj.value == xtob('')
+
+        with self.assertRaises(TypeError):
+            OctetString(1)
+
+    def test_octet_string_octet_string(self):
+        if _debug: TestOctetString._debug("test_octet_string_octet_string")
+
+        obj = OctetString(xtob('01'))
+        assert obj.value == xtob('01')
+        assert str(obj) == "OctetString(X'01')"
+
+        obj = OctetString(xtob('01020304'))
+        assert obj.value == xtob('01020304')
+        assert str(obj) == "OctetString(X'01020304')"
+
+    def test_octet_string_tag(self):
+        if _debug: TestOctetString._debug("test_octet_string_tag")
+
+        tag = Tag(Tag.applicationTagClass, Tag.octetStringAppTag, 1, xtob('00'))
+        obj = OctetString(tag)
+        assert obj.value == xtob('00')
+
+        tag = Tag(Tag.applicationTagClass, Tag.booleanAppTag, 0, xtob(''))
+        with self.assertRaises(ValueError):
+            OctetString(tag)
+
+        tag = Tag(Tag.contextTagClass, 0, 1, xtob('ff'))
+        with self.assertRaises(ValueError):
+            OctetString(tag)
+
+        tag = Tag(Tag.openingTagClass, 0)
+        with self.assertRaises(ValueError):
+            OctetString(tag)
+
+    def test_octet_string_copy(self):
+        if _debug: TestOctetString._debug("test_octet_string_copy")
+
+        obj1 = OctetString(xtob('01'))
+        obj2 = OctetString(obj1)
+        assert obj2.value == xtob('01')
+
+    def test_octet_string_endec(self):
+        if _debug: TestOctetString._debug("test_octet_string_endec")
+
+        octet_string_endec('')
+        octet_string_endec('01')
+        octet_string_endec('0102')
+        octet_string_endec('010203')
+        octet_string_endec('01020304')