stage: add test for core live-artifacts stage

This commit adds some unit tests around the coreos live-artifcats
mono stage.

stages/test/test_coreos_live_artifacts_mono.py

@@ -0,0 +1,28 @@
+#!/usr/bin/python3
+
+import tempfile
+import textwrap
+
+import pytest
+
+STAGE_NAME = "org.osbuild.coreos.live-artifacts.mono"
+
+
+def test_get_os_features(tmp_path, stage_module):
+    cfg_path = tmp_path / "usr/share/coreos-installer/example-config.yaml"
+    cfg_path.parent.mkdir(parents=True)
+    cfg_path.write_text(textwrap.dedent("""\
+    # Fedora CoreOS stream
+    stream: name
+    # Manually specify the image URL
+    image-url: URL
+    """))
+    features = stage_module.get_os_features(tmp_path)
+    assert {
+        "installer-config": True,
+        "installer-config-directives": {
+            "stream": True,
+            "image-url": True,
+        },
+        "live-initrd-network": True,
+    } == features