diff --git a/sstv/command.py b/sstv/command.py
index 0e4de3c..42a5e1f 100644
--- a/sstv/command.py
+++ b/sstv/command.py
@@ -1,7 +1,7 @@
 """Parsing arguments and starting program from command line"""
 
 import argparse
-from sys import exit
+from sys import argv, exit
 
 from PIL import Image
 from soundfile import available_formats as available_audio_formats
@@ -25,13 +25,16 @@ examples:
   Start decoding SSTV signal at 50.5 seconds into the audio
     $ sstv -d audio.ogg -s 50.50"""
 
-    def __init__(self):
+    def __init__(self, shell_args=None):
         """Handle command line arguments"""
 
         self._audio_file = None
         self._output_file = None
 
-        self.args = self.parse_args()
+        if shell_args is None:
+            self.args = self.parse_args(argv[1:])
+        else:
+            self.args = self.parse_args(shell_args)
 
     def __enter__(self):
         return self
@@ -62,8 +65,6 @@ examples:
                             default=0.0, dest="skip")
         parser.add_argument("-V", "--version", action="version",
                             version=version)
-        parser.add_argument("-v", "--verbose", action="count", default=1,
-                            help="increase output to the terminal")
         parser.add_argument("--list-modes", action="store_true",
                             dest="list_modes",
                             help="list supported SSTV modes")
@@ -75,11 +76,11 @@ examples:
                             help="list supported image file formats")
         return parser
 
-    def parse_args(self):
+    def parse_args(self, shell_args):
         """Parse command line arguments"""
 
         parser = self.init_args()
-        args = parser.parse_args()
+        args = parser.parse_args(shell_args)
 
         self._audio_file = args.audio_file
         self._output_file = args.output_file
diff --git a/test/__init__.py b/test/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/test/data/m1.ogg b/test/data/m1.ogg
new file mode 100644
index 0000000..78164b1
Binary files /dev/null and b/test/data/m1.ogg differ
diff --git a/test/test_command.py b/test/test_command.py
new file mode 100644
index 0000000..1a46bcf
--- /dev/null
+++ b/test/test_command.py
@@ -0,0 +1,64 @@
+"""Test cases for the CLI code"""
+
+import sys
+import unittest
+from io import StringIO
+
+from sstv.command import SSTVCommand
+
+
+class SSTVCommandTestCase(unittest.TestCase):
+    """Test SSTVCommand class"""
+
+    def setUp(self):
+        """Capture standard input/error using StringIO instance"""
+        sys.stdout = StringIO()
+        sys.stderr = StringIO()
+
+    def tearDown(self):
+        """Reset standard output/error"""
+        sys.stdout = sys.__stdout__
+        sys.stderr = sys.__stderr__
+
+    def test_arg_parser_output(self):
+        """Test --list-modes flag outputs correctly"""
+        with self.assertRaises(SystemExit):
+            SSTVCommand(["--list-modes"])
+        modes = "Supported modes: Robot 36, Robot 72, Martin 2, Martin 1, Scottie 2, Scottie 1, Scottie DX"
+        self.assertEqual(sys.stdout.getvalue().strip(), modes, "List of modes not equal")
+
+    def test_arg_parser_decode_error(self):
+        """Test decode flag with no input"""
+        with self.assertRaises(SystemExit):
+            SSTVCommand(["-d"])
+        self.assertIn("expected one argument", sys.stderr.getvalue().strip(),
+                      "Wrong argument error message not present in output")
+
+        with self.assertRaises(SystemExit):
+            SSTVCommand(["--decode"])
+        self.assertIn("expected one argument", sys.stderr.getvalue().strip(),
+                      "'Wrong argument' error message not present in output")
+
+        with self.assertRaises(SystemExit):
+            SSTVCommand(["-d", "./test/data/abc123"])
+        self.assertIn("No such file or directory", sys.stderr.getvalue().strip(),
+                      "'No file' error message not present in output")
+
+    def test_arg_parser_decode_success(self):
+        """Test decode flag with no input"""
+        args = SSTVCommand(["-d", "./test/data/m1.ogg"]).args
+        self.assertTrue(hasattr(args, "audio_file"),
+                        "audio_file attribute not set")
+        self.assertEqual(args.audio_file.name, "./test/data/m1.ogg",
+                         "Audio file name not set correctly")
+        self.assertTrue(hasattr(args, "skip"),
+                        "skip attribute not set")
+        self.assertEqual(args.skip, 0.0,
+                         "skip value not set to default value")
+
+    def test_arg_parser_decode_set_skip(self):
+        args = SSTVCommand(["-d", "./test/data/m1.ogg", "-s", "15.50"]).args
+        self.assertTrue(hasattr(args, "skip"),
+                        "skip attribute not set")
+        self.assertEqual(args.skip, 15.5,
+                         "skip value not set correctly")
diff --git a/test/test_decoder.py b/test/test_decoder.py
new file mode 100644
index 0000000..7547c92
--- /dev/null
+++ b/test/test_decoder.py
@@ -0,0 +1,28 @@
+"""Test cases for the decoder code"""
+
+import sys
+import unittest
+
+from sstv.decode import barycentric_peak_interp, calc_lum, SSTVDecoder
+
+
+class SSTVDecoderTestCase(unittest.TestCase):
+    """Test SSTVDecoder class"""
+
+    def test_calc_lum(self):
+        self.assertEqual(calc_lum(1450), 0)
+        self.assertEqual(calc_lum(2350), 255)
+        self.assertEqual(calc_lum(1758.1531), 82)
+
+    def test_barycentric_peak_interp(self):
+        bins = [100, 50, 0, 25, 50, 75, 100, 200, 150, 100]
+        # Left neighbour is higher, so result must be smaller/equal
+        self.assertLess(barycentric_peak_interp(bins, 9), 9)
+        # Right neighbour is smaller and no left, so it must be smaller
+        self.assertLessEqual(barycentric_peak_interp(bins, 0), 0)
+        # Right neighbour is larger than left, so x must increase
+        self.assertGreaterEqual(barycentric_peak_interp(bins, 7), 7)
+
+        bins = [1, 2, 2, 2, 1]
+        # Centre 2 surrounded by 2s should result in no change
+        self.assertEqual(barycentric_peak_interp(bins, 2), 2)