diff --git a/pyodide_lock/cli.py b/pyodide_lock/cli.py
index af3c28e..dae782f 100644
--- a/pyodide_lock/cli.py
+++ b/pyodide_lock/cli.py
@@ -47,7 +47,7 @@ def add_wheels(
 
     """
     sp = PyodideLockSpec.from_json(input)
-    add_wheels_to_spec(
+    sp = add_wheels_to_spec(
         sp,
         wheels,
         base_path=base_path,
diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..41ec6d1
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,26 @@
+from pathlib import Path
+import gzip
+import shutil
+
+from typer.testing import CliRunner
+from pyodide_lock.cli import main
+
+DATA_DIR = Path(__file__).parent / "data"
+
+
+runner = CliRunner()
+
+def test_cli_modify_file(test_wheel_list, tmp_path):
+    source_path = DATA_DIR / f"pyodide-lock-0.23.3.json.gz"
+    target_path = tmp_path / "pyodide-lock.json"
+    new_lock_path = tmp_path / "pyodide-lock.json"
+
+    with gzip.open(source_path) as fh_in:
+        with target_path.open("wb") as fh_out:
+            shutil.copyfileobj(fh_in, fh_out)
+
+    result = runner.invoke(main, ["--input="+str(target_path), "--output="+str(new_lock_path), str(test_wheel_list[0])])
+    assert result.exit_code == 0
+    assert target_path.read_text() != new_lock_path.read_text()
+
+    
\ No newline at end of file