stages(dracut): add small unittest for initoverlayfs

Small followup for https://github.com/osbuild/osbuild/pull/1586
that includes a basic check that the initoverlayfs option calls
the right binary.

stages/test/test_dracut.py

@@ -0,0 +1,30 @@
+#!/usr/bin/python3
+
+from unittest.mock import patch
+
+import pytest
+
+STAGE_NAME = "org.osbuild.dracut"
+
+
+@pytest.mark.parametrize("with_initoverlayfs,expected_argv2", [
+    (False, "/usr/bin/dracut"),
+    (True, "/usr/bin/initoverlayfs-install"),
+])
+@patch("subprocess.run")
+def test_dracut_with_initoverlayfs(mocked_run, tmp_path, stage_module, with_initoverlayfs, expected_argv2):
+    options = {
+        "kernel": [
+            "5.14.0-247.el9.x86_64"
+        ],
+        "initoverlayfs": with_initoverlayfs,
+    }
+
+    stage_module.main(tmp_path, options)
+
+    assert len(mocked_run.call_args_list) == 1
+    args, kwargs = mocked_run.call_args_list[0]
+    assert kwargs.get("check") is True
+    run_argv = args[0]
+    assert run_argv[0] == "/usr/sbin/chroot"
+    assert run_argv[2] == expected_argv2