backend-test-utils: sync feature compat unwrapping

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/dry-horses-report.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-test-utils': patch
+---
+
+Sync feature installation compatibility logic with `@backstage/backend-app-api`.

packages/backend-test-utils/src/next/wiring/TestBackend.ts

@@ -209,10 +209,19 @@ function isPromise<T>(value: unknown | Promise<T>): value is Promise<T> {
   );
 }
 
+// Same as in the backend-app-api, handles double defaults from dynamic imports
 function unwrapFeature(
-  feature: BackendFeature | (() => BackendFeature),
+  feature: BackendFeature | { default: BackendFeature },
 ): BackendFeature {
-  return typeof feature === 'function' ? feature() : feature;
+  if ('$$type' in feature) {
+    return feature;
+  }
+
+  if ('default' in feature) {
+    return feature.default;
+  }
+
+  return feature;
 }
 
 const backendInstancesToCleanUp = new Array<Backend>();