diff --git a/tests/decryption/test_decrypt.py b/tests/decryption/test_decrypt.py
index e502718..c579eb6 100644
--- a/tests/decryption/test_decrypt.py
+++ b/tests/decryption/test_decrypt.py
@@ -1,6 +1,8 @@
 """Tests for decrypt.py"""
+import os
 from pathlib import Path
 import shutil
+from unittest import mock
 
 from crypt4gh.keys import get_private_key as get_sk_bytes, get_public_key as get_pk_bytes
 import pytest
@@ -8,8 +10,10 @@
 from crypt4gh_middleware.decrypt import (
     get_private_keys,
     decrypt_files,
-    move_files
+    move_files,
+    get_args
 )
+from tests.utils import patch_cli
 
 INPUT_DIR = Path(__file__).parents[2]/"inputs"
 INPUT_TEXT = "hello world from the input!"
@@ -145,3 +149,41 @@ def test_permission_error(self, tmp_path):
         output_dir.chmod(0o400)
         with pytest.raises(PermissionError):
             move_files(file_paths=[INPUT_DIR/"hello.txt"], output_dir=output_dir)
+
+
+class TestGetArgs:
+    """Test get_args."""
+
+    def test_get_args(self):
+        """Test that the arguments are parsed correctly."""
+        with patch_cli(["decrypt.py", "--output-dir", "dir", "file.txt"]):
+            args = get_args()
+            assert args.output_dir == Path("dir")
+            assert args.file_paths == [Path("file.txt")]
+
+    def test_multiple_files(self):
+        """Test that multiple file paths can be passed."""
+        files = ["file.txt", "file2.txt", "file3.txt"]
+        with patch_cli(["decrypt.py"] + files):
+            args = get_args()
+            assert args.file_paths == [Path(file) for file in files]
+
+    def test_default_output_dir(self):
+        """Test that output_dir defaults to $TMPDIR when no directory is passed."""
+        with (patch_cli(["decrypt.py", "file.txt"]),
+              mock.patch.dict(os.environ, {"TMPDIR": "/mock/tmpdir"})):
+            args = get_args()
+            assert args.output_dir == Path("/mock/tmpdir")
+            assert args.file_paths == [Path("file.txt")]
+
+    def test_invalid_argument(self):
+        """Test that a system exit occurs when an invalid argument is passed."""
+        with (patch_cli(["decrypt.py", "--bad-argument", "dir", "file.txt"]),
+              pytest.raises(SystemExit)):
+            get_args()
+
+    def test_no_file_paths(self):
+        """Test that a system exit occurs when no file paths are passed."""
+        with (patch_cli(["decrypt.py", "--output-dir", "dir"]),
+              pytest.raises(SystemExit)):
+            get_args()
diff --git a/tests/utils.py b/tests/utils.py
index fbc38d6..3a37831 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -1,6 +1,15 @@
 """ Utility functions for tests."""
 from functools import wraps
+import contextlib
 import signal
+from unittest import mock
+
+
+@contextlib.contextmanager
+def patch_cli(args):
+    """Context manager that patches sys.argv."""
+    with mock.patch("sys.argv", args):
+        yield
 
 
 def timeout(time_limit):