Add a test to extend using an empty service (placeholder)

Signed-off-by: Natanael Arndt <arndtn@gmail.com>

tests/extends_w_empty_service/common-services.yml

@@ -0,0 +1,7 @@
+services:
+  webapp_default:
+
+  webapp_special:
+    image: busybox
+    volumes:
+      - "/data"

tests/extends_w_empty_service/docker-compose.yml

@@ -0,0 +1,10 @@
+version: "3"
+services:
+  web:
+    image: busybox
+    extends:
+      file: common-services.yml
+      service: webapp_default
+    environment:
+      - DEBUG=1
+    cpu_shares: 5

tests/test_podman_compose.py

@@ -59,3 +59,26 @@ def test_podman_compose_extends_w_file_subdir():
     out, _, returncode = capture(command_check_container)
     assert 0 == returncode
     assert out == b""
+
+
+def test_podman_compose_extends_w_empty_service():
+    """
+    Test that podman-compose can execute podman-compose -f <file> up with extended File which
+    includes an empty service. (e.g. if the file is used as placeholder for more complex configurations.)
+    :return:
+    """
+    main_path = Path(__file__).parent.parent
+
+    command_up = [
+        "python3",
+        str(main_path.joinpath("podman_compose.py")),
+        "-f",
+        str(
+            main_path.joinpath("tests", "extends_w_empty_service", "docker-compose.yml")
+        ),
+        "up",
+        "-d",
+    ]
+
+    _, _, returncode = capture(command_up)
+    assert 0 == returncode