diff --git a/tools/test_post_process_props.py b/tools/test_post_process_props.py
new file mode 100644
index 0000000..8a9c3ed
--- /dev/null
+++ b/tools/test_post_process_props.py
@@ -0,0 +1,230 @@
+#!/usr/bin/env python3
+#
+# 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.
+
+import contextlib
+import io
+import unittest
+
+from unittest.mock import *
+from post_process_props import *
+
+class PropTestCase(unittest.TestCase):
+  def test_createFromLine(self):
+    p = Prop.from_line("# this is comment")
+    self.assertTrue(p.is_comment())
+    self.assertEqual("", p.name)
+    self.assertEqual("", p.value)
+    self.assertFalse(p.is_optional())
+    self.assertEqual("# this is comment", str(p))
+
+    for line in ["a=b", "a = b", "a= b", "a =b", "  a=b   "]:
+      p = Prop.from_line(line)
+      self.assertFalse(p.is_comment())
+      self.assertEqual("a", p.name)
+      self.assertEqual("b", p.value)
+      self.assertFalse(p.is_optional())
+      self.assertEqual("a=b", str(p))
+
+    for line in ["a?=b", "a ?= b", "a?= b", "a ?=b", "  a?=b   "]:
+      p = Prop.from_line(line)
+      self.assertFalse(p.is_comment())
+      self.assertEqual("a", p.name)
+      self.assertEqual("b", p.value)
+      self.assertTrue(p.is_optional())
+      self.assertEqual("a?=b", str(p))
+
+  def test_makeAsComment(self):
+    p = Prop.from_line("a=b")
+    p.comments.append("# a comment")
+    self.assertFalse(p.is_comment())
+
+    p.make_as_comment()
+    self.assertTrue(p.is_comment())
+    self.assertTrue("# a comment\n#a=b", str(p))
+
+class PropListTestcase(unittest.TestCase):
+  def setUp(self):
+    content = """
+    # comment
+    foo=true
+    bar=false
+    qux?=1
+    # another comment
+    foo?=false
+    """
+    self.patcher = patch("post_process_props.open", mock_open(read_data=content))
+    self.mock_open = self.patcher.start()
+    self.props = PropList("file")
+
+  def tearDown(self):
+    self.patcher.stop()
+    self.props = None
+
+  def test_readFromFile(self):
+    self.assertEqual(4, len(self.props.get_all_props()))
+    expected = [
+        ("foo", "true", False),
+        ("bar", "false", False),
+        ("qux", "1", True),
+        ("foo", "false", True)
+    ]
+    for i,p in enumerate(self.props.get_all_props()):
+      self.assertEqual(expected[i][0], p.name)
+      self.assertEqual(expected[i][1], p.value)
+      self.assertEqual(expected[i][2], p.is_optional())
+      self.assertFalse(p.is_comment())
+
+    self.assertEqual(set(["foo", "bar", "qux"]), self.props.get_all_names())
+
+    self.assertEqual("true", self.props.get_value("foo"))
+    self.assertEqual("false", self.props.get_value("bar"))
+    self.assertEqual("1", self.props.get_value("qux"))
+
+    # there are two assignments for 'foo'
+    self.assertEqual(2, len(self.props.get_props("foo")))
+
+  def test_putNewProp(self):
+    self.props.put("new", "30")
+
+    self.assertEqual(5, len(self.props.get_all_props()))
+    last_prop = self.props.get_all_props()[-1]
+    self.assertEqual("new", last_prop.name)
+    self.assertEqual("30", last_prop.value)
+    self.assertFalse(last_prop.is_optional())
+
+  def test_putExistingNonOptionalProp(self):
+    self.props.put("foo", "NewValue")
+
+    self.assertEqual(4, len(self.props.get_all_props()))
+    foo_prop = self.props.get_props("foo")[0]
+    self.assertEqual("foo", foo_prop.name)
+    self.assertEqual("NewValue", foo_prop.value)
+    self.assertFalse(foo_prop.is_optional())
+    self.assertEqual("# Value overridden by post_process_props.py. " +
+                     "Original value: true\nfoo=NewValue", str(foo_prop))
+
+  def test_putExistingOptionalProp(self):
+    self.props.put("qux", "2")
+
+    self.assertEqual(5, len(self.props.get_all_props()))
+    last_prop = self.props.get_all_props()[-1]
+    self.assertEqual("qux", last_prop.name)
+    self.assertEqual("2", last_prop.value)
+    self.assertFalse(last_prop.is_optional())
+    self.assertEqual("# Auto-added by post_process_props.py\nqux=2",
+                     str(last_prop))
+
+  def test_deleteNonOptionalProp(self):
+    props_to_delete = self.props.get_props("foo")[0]
+    props_to_delete.delete(reason="testing")
+
+    self.assertEqual(3, len(self.props.get_all_props()))
+    self.assertEqual("# Removed by post_process_props.py because testing\n" +
+                     "#foo=true", str(props_to_delete))
+
+  def test_deleteOptionalProp(self):
+    props_to_delete = self.props.get_props("qux")[0]
+    props_to_delete.delete(reason="testing")
+
+    self.assertEqual(3, len(self.props.get_all_props()))
+    self.assertEqual("# Removed by post_process_props.py because testing\n" +
+                     "#qux?=1", str(props_to_delete))
+
+  def test_overridingNonOptional(self):
+    props_to_be_overridden = self.props.get_props("foo")[1]
+    self.assertTrue("true", props_to_be_overridden.value)
+
+    self.assertTrue(override_optional_props(self.props))
+
+    # size reduced to 3 because foo?=false was overridden by foo=true
+    self.assertEqual(3, len(self.props.get_all_props()))
+
+    self.assertEqual(1, len(self.props.get_props("foo")))
+    self.assertEqual("true", self.props.get_props("foo")[0].value)
+
+    self.assertEqual("# Removed by post_process_props.py because " +
+                     "overridden by foo=true\n#foo?=false",
+                     str(props_to_be_overridden))
+
+  def test_overridingOptional(self):
+    content = """
+    # comment
+    qux?=2
+    foo=true
+    bar=false
+    qux?=1
+    # another comment
+    foo?=false
+    """
+    with patch('post_process_props.open', mock_open(read_data=content)) as m:
+      props = PropList("hello")
+
+      props_to_be_overridden = props.get_props("qux")[0]
+      self.assertEqual("2", props_to_be_overridden.value)
+
+      self.assertTrue(override_optional_props(props))
+
+      self.assertEqual(1, len(props.get_props("qux")))
+      self.assertEqual("1", props.get_props("qux")[0].value)
+      # the only left optional assignment becomes non-optional
+      self.assertFalse(props.get_props("qux")[0].is_optional())
+
+      self.assertEqual("# Removed by post_process_props.py because " +
+                       "overridden by qux?=1\n#qux?=2",
+                       str(props_to_be_overridden))
+
+  def test_overridingDuplicated(self):
+    content = """
+    # comment
+    foo=true
+    bar=false
+    qux?=1
+    foo=false
+    # another comment
+    foo?=false
+    """
+    with patch("post_process_props.open", mock_open(read_data=content)) as m:
+      stderr_redirect = io.StringIO()
+      with contextlib.redirect_stderr(stderr_redirect):
+        props = PropList("hello")
+
+        # fails due to duplicated foo=true and foo=false
+        self.assertFalse(override_optional_props(props))
+
+        self.assertEqual("error: found duplicate sysprop assignments:\n" +
+                         "foo=true\nfoo=false\n", stderr_redirect.getvalue())
+
+  def test_overridingDuplicatedWithSameValue(self):
+    content = """
+    # comment
+    foo=true
+    bar=false
+    qux?=1
+    foo=true
+    # another comment
+    foo?=false
+    """
+    with patch("post_process_props.open", mock_open(read_data=content)) as m:
+      stderr_redirect = io.StringIO()
+      with contextlib.redirect_stderr(stderr_redirect):
+        props = PropList("hello")
+
+        # we have duplicated foo=true and foo=true, but that's allowed
+        # since they have the same value
+        self.assertTrue(override_optional_props(props))
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)