diff --git a/.github/workflows/compile.yml b/.github/workflows/compile.yml
index 47b7fcb..449d4be 100644
--- a/.github/workflows/compile.yml
+++ b/.github/workflows/compile.yml
@@ -41,6 +41,11 @@ jobs:
           cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -DBUILD_NO_SUBFOLDERS=1
           cmake --build build --config Release
 
+      # Run tests
+      - name: Tests
+        run: |
+          ctest --test-dir build --build-config Release
+
       # Gather documentation and executables to a common directory
       # Ignore copying errors from only one of build/jpegoptim or build/jpegoptim.exe existing
       - name: Prepare files
diff --git a/.gitignore b/.gitignore
index f38b007..f4d1d93 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,5 @@ jpegoptim.prn
 jpegoptim.ps
 jpegoptim.txt
 *.o
-*.jpg
 build/
 autom4te.cache/
diff --git a/CMakeLists.txt b/CMakeLists.txt
index a42ba8d..2798b6a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -447,3 +447,17 @@ if(ARITH_ENABLED)
 else()
     message(STATUS "Arithmetic Coding: Disabled")
 endif()
+
+
+
+find_package(Python3 COMPONENTS Interpreter Development)
+
+if (Python3_FOUND)
+  enable_testing()
+  add_test(NAME unittests
+	 COMMAND ${Python3_EXECUTABLE} test.py
+	 WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/test
+	 )
+
+  set_property(TEST unittests PROPERTY ENVIRONMENT "JPEGOPTIM=$<TARGET_FILE:jpegoptim>")
+endif()
diff --git a/Makefile.in b/Makefile.in
index 9e3b30f..a238cae 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -43,6 +43,7 @@ LDFLAGS   = @LDFLAGS@
 LIBS      = @LIBS@
 STRIP     = strip
 
+PYTHON ?= python3
 
 INSTALL = @INSTALL@
 INSTALL_DATA = @INSTALL_DATA@
@@ -58,6 +59,8 @@ DISTNAME  = $(PKGNAME)-$(Version)
 
 OBJS = $(PKGNAME).o jpegdest.o jpegsrc.o jpegmarker.o misc.o @GNUGETOPT@
 
+.PHONY: test
+
 all:	$(PKGNAME)
 
 dssim.o:	dssim.c
@@ -107,4 +110,7 @@ love:
 spell:
 	codespell -S .git -S tools
 
+test:	all
+	(cd test && $(PYTHON) test.py -v)
+
 # eof
diff --git a/test/README b/test/README
new file mode 100644
index 0000000..acb6cde
--- /dev/null
+++ b/test/README
@@ -0,0 +1,13 @@
+Test images for jpegoptim.
+
+Copyright 2023 by Timo Kokkonen.
+These images are licensed under CC BY-NC-SA 4.0.
+
+To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/4.0/
+
+
+jpegoptim_test1.jpg: Test image created with Photoshop using generative AI.
+jpegoptim_test2.jpg: Test image scaled down and already optimized.
+
+
+
diff --git a/test/jpegoptim_test1.jpg b/test/jpegoptim_test1.jpg
new file mode 100644
index 0000000..ce8ec6e
Binary files /dev/null and b/test/jpegoptim_test1.jpg differ
diff --git a/test/jpegoptim_test2-broken.jpg b/test/jpegoptim_test2-broken.jpg
new file mode 100644
index 0000000..f77fced
Binary files /dev/null and b/test/jpegoptim_test2-broken.jpg differ
diff --git a/test/jpegoptim_test2.jpg b/test/jpegoptim_test2.jpg
new file mode 100644
index 0000000..ee0a3fd
Binary files /dev/null and b/test/jpegoptim_test2.jpg differ
diff --git a/test/test.py b/test/test.py
new file mode 100755
index 0000000..d8ce86f
--- /dev/null
+++ b/test/test.py
@@ -0,0 +1,109 @@
+#!/usr/bin/env python3
+#
+# test.py -- Unit tests for jpegoptim
+#
+# Copyright (C) 2023 Timo Kokkonen <tjko@iki.fi>
+#
+# 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 3 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/>.
+#
+
+"""jpegoptim unit tester"""
+
+import os
+import subprocess
+import unittest
+
+
+class JpegoptimTests(unittest.TestCase):
+    """jpegoptim test cases"""
+
+    program = '../jpegoptim'
+    debug = False
+
+    def setUp(self):
+        if "JPEGOPTIM" in os.environ:
+            self.program = os.environ["JPEGOPTIM"]
+
+    def run_test(self, args, check=True, directory=None):
+        """execute jpegoptim for a test"""
+        command = [self.program] + args
+        if directory:
+            if not os.path.isdir(directory):
+                os.makedirs(directory)
+            command.extend(['-o', '-d', directory])
+        if self.debug:
+            print(f'\nRun command: {" ".join(command)}')
+        res = subprocess.run(command, encoding="utf-8", check=check,
+                             stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+        output = res.stdout
+        if self.debug:
+            print(f'Result: {res.returncode}')
+            print(f'---\n{output}\n---\n')
+        return output, res.returncode
+
+
+    def test_version(self):
+        """test version information output"""
+        output, _ = self.run_test(['--version'])
+        self.assertIn('GNU General Public License', output)
+        self.assertRegex(output, r'jpegoptim v\d+\.\d+\.\d+')
+
+    def test_noarguments(self):
+        """test running withouth arguments"""
+        output, res = self.run_test([], check=False)
+        self.assertEqual(1, res)
+        self.assertRegex(output, r'file argument\(?s\)? missing')
+
+    def test_default(self):
+        """test default optimization"""
+        output, _ = self.run_test(['jpegoptim_test1.jpg'], directory='tmp/default')
+        self.assertRegex(output, r'\s\[OK\]\s.*\soptimized\.\s*$')
+        # check that output file is indeed smaller than the input file
+        self.assertGreater(os.path.getsize('jpegoptim_test1.jpg'),
+                           os.path.getsize('tmp/default/jpegoptim_test1.jpg'))
+
+        # check that output file is valid and "optimized"
+        output, _ = self.run_test(['-n', 'tmp/default/jpegoptim_test1.jpg'])
+        self.assertRegex(output, r'\s\[OK\]\s.*\sskipped\.\s*$')
+
+    def test_lossy(self):
+        """test lossy optimization"""
+        output, _ = self.run_test(['-m', '10', 'jpegoptim_test1.jpg'],
+                                  directory='tmp/lossy')
+        self.assertRegex(output, r'\s\[OK\]\s.*\soptimized\.\s*$')
+        # check that output file is indeed smaller than the input file
+        self.assertGreater(os.path.getsize('jpegoptim_test1.jpg'),
+                           os.path.getsize('tmp/lossy/jpegoptim_test1.jpg'))
+
+        # check that output file is valid and "optimized"
+        output, _ = self.run_test(['-n', 'tmp/lossy/jpegoptim_test1.jpg'])
+        self.assertRegex(output, r'\s\[OK\]\s.*\sskipped\.\s*$')
+
+    def test_optimized(self):
+        """test already optimized image"""
+        output, _ = self.run_test(['jpegoptim_test2.jpg'],
+                                  directory='tmp/optimized')
+        self.assertRegex(output, r'\s\[OK\]\s.*\sskipped\.\s*$')
+
+    def test_broken(self):
+        """test broken image"""
+        output, _ = self.run_test(['jpegoptim_test2-broken.jpg'],
+                                    directory='tmp/broken', check=False)
+        self.assertRegex(output, r'\s\[WARNING\]\s.*\sskipped\.\s*$')
+
+
+if __name__ == '__main__':
+    unittest.main()
+
+# eof :-)