diff --git a/scripts/paycheck_unittest.py b/scripts/paycheck_unittest.py
new file mode 100755
index 0000000..a90d269
--- /dev/null
+++ b/scripts/paycheck_unittest.py
@@ -0,0 +1,105 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2020 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.
+#
+
+"""Unit testing paycheck.py."""
+
+# This test requires new (Y) and old (X) images, as well as a full payload
+# from image Y and a delta payload from Y to X for each partition.
+# Payloads are from sample_images/generate_payloads.
+#
+# The test performs the following:
+#
+# - It statically applies the full and delta payloads.
+#
+# - It applies full_payload to yield a new kernel (kern.part) and rootfs
+#   (root.part) and compares them to the new image partitions.
+#
+# - It applies delta_payload to the old image to yield a new kernel and rootfs
+#   and compares them to the new image partitions.
+#
+# Previously test_paycheck.sh. Run with update_payload ebuild.
+
+# Disable check for function names to avoid errors based on old code
+# pylint: disable=invalid-name
+
+import filecmp
+import os
+import subprocess
+import unittest
+
+
+class PaycheckTest(unittest.TestCase):
+  """Test paycheck functions."""
+
+  def setUp(self):
+    self.tmpdir = os.getenv('T')
+
+    self._full_payload = os.path.join(self.tmpdir, 'full_payload.bin')
+    self._delta_payload = os.path.join(self.tmpdir, 'delta_payload.bin')
+
+    self._new_kernel = os.path.join(self.tmpdir, 'disk_ext2_4k.img')
+    self._new_root = os.path.join(self.tmpdir, 'disk_sqfs_default.img')
+    self._old_kernel = os.path.join(self.tmpdir,
+                                    'disk_ext2_4k_empty.img')
+    self._old_root = os.path.join(self.tmpdir, 'disk_sqfs_empty.img')
+
+    # Temp output files.
+    self._kernel_part = os.path.join(self.tmpdir, 'kern.part')
+    self._root_part = os.path.join(self.tmpdir, 'root.part')
+
+  def checkPayload(self, type_arg, payload):
+    """Checks Payload."""
+    self.assertEqual(0, subprocess.check_call(['./paycheck.py', '-t',
+                                               type_arg, payload]))
+
+  def testFullPayload(self):
+    """Checks the full payload statically."""
+    self.checkPayload('full', self._full_payload)
+
+  def testDeltaPayload(self):
+    """Checks the delta payload statically."""
+    self.checkPayload('delta', self._delta_payload)
+
+  def testApplyFullPayload(self):
+    """Applies full payloads and compares results to new sample images."""
+    self.assertEqual(0, subprocess.check_call(['./paycheck.py',
+                                               self._full_payload,
+                                               '--part_names', 'kernel', 'root',
+                                               '--out_dst_part_paths',
+                                               self._kernel_part,
+                                               self._root_part]))
+
+    # Check if generated full image is equal to sample image.
+    self.assertTrue(filecmp.cmp(self._kernel_part, self._new_kernel))
+    self.assertTrue(filecmp.cmp(self._root_part, self._new_root))
+
+  def testApplyDeltaPayload(self):
+    """Applies delta to old image and checks against new sample images."""
+    self.assertEqual(0, subprocess.check_call(['./paycheck.py',
+                                               self._delta_payload,
+                                               '--part_names', 'kernel', 'root',
+                                               '--src_part_paths',
+                                               self._old_kernel, self._old_root,
+                                               '--out_dst_part_paths',
+                                               self._kernel_part,
+                                               self._root_part]))
+
+    self.assertTrue(filecmp.cmp(self._kernel_part, self._new_kernel))
+    self.assertTrue(filecmp.cmp(self._root_part, self._new_root))
+
+if __name__ == '__main__':
+  unittest.main()