Add agent.base_image setting in system test configuration file (#788)

Co-authored-by: Jaime Soriano Pastor <jaime.soriano@elastic.co>

spec/changelog.yml

@@ -20,6 +20,9 @@
   - description: Improved error message for unsupported package types.
     type: enhancement
     link: https://github.com/elastic/package-spec/pull/777
+  - description: Add new agent.base_image setting for system tests configuration files.
+    type: enhancement
+    link: https://github.com/elastic/package-spec/pull/788
 - version: 3.2.1
   changes:
   - description: Improve error information for missing dataset field in manifest.

spec/integration/data_stream/_dev/test/system/config.spec.yml

@@ -34,6 +34,17 @@ spec:
           enum:
             - docker
           default: docker
+        base_image:
+          description: >
+            Elastic Agent image to be used for testing. Setting `default` will be used the
+            same Elastic Agent image as the stack. Setting `complete` will use the "complete"
+            image, that includes all supported collectors, a web browser and the required runtime
+            for synthetic testing.
+          type: string
+          enum:
+            - default
+            - complete
+          default: "default"
         user:
           description: "User that runs the Elastic Agent process"
           type: string

test/packages/good_v3/data_stream/agent_settings/_dev/test/system/test-default-config.yml

@@ -2,6 +2,7 @@ wait_for_data_timeout: 10m
 vars: ~
 agent:
   runtime: docker
+  base_image: complete
   user: root
   pid_mode: host
   linux_capabilities: