container-cross-install: add tests and documentation for custom service filescontainer-cross-install

Add pytest tests to verify CONTAINER_SERVICE_FILE varflag support:

TestCustomServiceFileSupport (unit tests, no build required):
- test_bbclass_has_service_file_support
- test_bundle_class_has_service_file_support
- test_service_file_map_syntax
- test_install_custom_service_function

TestCustomServiceFileBoot (boot tests, require built image):
- test_systemd_services_directory_exists
- test_container_services_present
- test_container_service_enabled
- test_custom_service_content
- test_podman_quadlet_directory

Documentation updates:
- docs/container-bundling.md: Add "Custom Service Files" section with
  variable format, usage examples for both BUNDLED_CONTAINERS and
  container-bundle packages, and example .service/.container files
- tests/README.md: Add test class entries to structure diagram and
  "What the Tests Check" table

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/tests/README.md b/tests/README.md
index 4f5aed28..09bc70ca 100644
--- a/tests/README.md
+++ b/tests/README.md
@@ -162,6 +162,8 @@ BBMULTICONFIG = "vruntime-aarch64 vruntime-x86-64"
 | `TestVdkrRecipes` | vdkr recipe builds | `bitbake vcontainer-tarball` |
 | `TestMulticonfig` | Multiconfig setup | `BBMULTICONFIG` configured |
 | `TestBundledContainersBoot` | **Boot image and verify containers** | Full image with Docker/Podman |
+| `TestCustomServiceFileSupport` | CONTAINER_SERVICE_FILE varflag support | None (file check only) |
+| `TestCustomServiceFileBoot` | Custom service files installed correctly | Full image with autostart containers |
 
 ### Boot Tests (TestBundledContainersBoot)
 
@@ -440,7 +442,9 @@ tests/
 │   ├── TestBundledContainers        # end-to-end bundling
 │   ├── TestVdkrRecipes              # vdkr builds
 │   ├── TestMulticonfig              # multiconfig setup
-│   └── TestBundledContainersBoot    # boot and verify containers
+│   ├── TestBundledContainersBoot    # boot and verify containers
+│   ├── TestCustomServiceFileSupport # CONTAINER_SERVICE_FILE varflag support
+│   └── TestCustomServiceFileBoot    # custom service file boot verification
 ├── test_multiarch_oci.py            # Multi-architecture OCI tests
 │   ├── TestOCIImageIndexDetection   # multi-arch OCI detection
 │   ├── TestPlatformSelection        # arch selection (aarch64/x86_64)