diff --git a/tools/releasetools/test_ota_utils.py b/tools/releasetools/test_ota_utils.py
new file mode 100644
index 0000000..9a82e6f
--- /dev/null
+++ b/tools/releasetools/test_ota_utils.py
@@ -0,0 +1,56 @@
+# Copyright (C) 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import unittest
+import io
+import ota_utils
+import zipfile
+
+
+class TestZipEntryOffset(unittest.TestCase):
+  def test_extra_length_differ(self):
+      # This is a magic zip file such that:
+      # 1. It has 1 entry, `file.txt'`
+      # 2. The central directory entry for the entry contains an extra field of#
+      # length 24, while the local file header for the entry contains an extra#
+      # field of length 28.
+      # It is key that the entry contains extra field of different length.
+      # The sole purpose of this test case is make sure our offset computing
+      # logic works in this scenario.
+
+      # This is created by:
+      # touch file.txt
+      # zip -0 test.zip file.txt
+      # Above command may or may not work on all platforms.
+      # Some zip implementation will keep the extra field size consistent.
+      # Some don't
+    magic_zip = b'PK\x03\x04\n\x00\x00\x00\x00\x00nY\xfcR\x00\x00\x00\x00\x00\x00\x00' +\
+        b'\x00\x00\x00\x00\x00\x08\x00\x1c\x00file.txtUT\t\x00\x03' +\
+        b'\xa0s\x01a\xa0s\x01aux\x0b\x00\x01\x04\x88\xc4\t\x00\x04S_\x01\x00' +\
+        b'PK\x01\x02\x1e\x03\n\x00\x00\x00\x00\x00nY\xfcR\x00\x00\x00\x00' +\
+        b'\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x18\x00\x00\x00\x00\x00' +\
+        b'\x00\x00\x00\x00\x80\x81\x00\x00\x00\x00file.txt' +\
+        b'UT\x05\x00\x03\xa0s\x01aux\x0b\x00\x01\x04\x88\xc4\t\x00\x04' +\
+        b'S_\x01\x00PK\x05\x06\x00\x00\x00\x00\x01\x00\x01\x00N\x00\x00' +\
+        b'\x00B\x00\x00\x00\x00\x00'
+    # Just making sure we concatenated the bytes correctly
+    self.assertEqual(len(magic_zip), 166)
+    fp = io.BytesIO(magic_zip)
+    with zipfile.ZipFile(fp, 'r') as zfp:
+      self.assertGreater(len(zfp.infolist()), 0)
+      zinfo = zfp.getinfo("file.txt")
+      (offset, size) = ota_utils.GetZipEntryOffset(zfp, zinfo)
+      self.assertEqual(size, zinfo.file_size)
+      self.assertEqual(offset, zipfile.sizeFileHeader+len(zinfo.filename) + 28)