ref to json

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

.changeset/rude-fireants-accept.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-plugin-api': patch
+---
+
+Add a `toJSON` on refs so that they can appear in expectations in jest tests

packages/backend-plugin-api/src/services/system/types.ts

@@ -17,7 +17,9 @@
 import { BackendFeature } from '../../types';
 
 /**
- * TODO
+ * A reference to a backend service. You can use these references to mark
+ * dependencies on services and having their implementations injected
+ * automatically.
  *
  * @public
  */
@@ -39,6 +41,11 @@ export type ServiceRef<
    */
   scope: TScope;
 
+  /**
+   * Marks whether the service is a multiton or not. Multiton services the
+   * opposite of singletons - they can be provided many times, and when depended
+   * on, you receive an array of all provided instances.
+   */
   multiton?: TInstances extends 'multiton' ? true : false;
 
   /**
@@ -142,6 +149,15 @@ export function createServiceRef<
     toString() {
       return `serviceRef{${options.id}}`;
     },
+    toJSON() {
+      // This avoids accidental calls to T happening e.g. in tests
+      return {
+        $$type: '@backstage/ServiceRef',
+        id,
+        scope,
+        multiton,
+      };
+    },
     $$type: '@backstage/ServiceRef',
     __defaultFactory: defaultFactory,
   } as ServiceRef<TService, typeof scope, TInstances> & {