feat(storage): support delete_source_objects in compose API (Address PR feedback)

- Removed unnecessary fixture usage in system test.
- Ensured destination metadata is not empty in unit test by setting content_type.
- verified end-to-end functionality in system test.

Reference PR: googleapis/google-cloud-java#12873

Co-authored-by: nidhiii-27 <224584462+nidhiii-27@users.noreply.github.com>

Author: google-labs-jules[bot]

packages/google-cloud-storage/tests/system/test_blob.py

@@ -853,24 +853,24 @@ def test_blob_compose_new_blob(shared_bucket, blobs_to_delete):
     assert destination.download_as_bytes() == payload_1 + payload_2
 
 
-def test_blob_compose_delete_source_objects(shared_bucket, blobs_to_delete):
+def test_blob_compose_delete_source_objects(shared_bucket):
     payload_1 = b"AAA\n"
     source_1 = shared_bucket.blob("source-1-delete")
     source_1.upload_from_string(payload_1)
-    blobs_to_delete.append(source_1)
 
     payload_2 = b"BBB\n"
     source_2 = shared_bucket.blob("source-2-delete")
     source_2.upload_from_string(payload_2)
-    blobs_to_delete.append(source_2)
 
     destination = shared_bucket.blob("destination-delete")
     destination.compose([source_1, source_2], delete_source_objects=True)
-    blobs_to_delete.append(destination)
 
-    assert destination.download_as_bytes() == payload_1 + payload_2
-    assert not source_1.exists()
-    assert not source_2.exists()
+    try:
+        assert destination.download_as_bytes() == payload_1 + payload_2
+        assert not source_1.exists()
+        assert not source_2.exists()
+    finally:
+        destination.delete()
 
 
 def test_blob_compose_new_blob_wo_content_type(shared_bucket, blobs_to_delete):

packages/google-cloud-storage/tests/unit/test_blob.py

@@ -4484,6 +4484,7 @@ def test_compose_w_delete_source_objects(self):
         source_1_name = "source-1"
         source_2_name = "source-2"
         destination_name = "destination"
+        content_type = "text/plain"
         delete_source_objects = True
         api_response = {}
         client = mock.Mock(spec=["_post_resource"])
@@ -4492,6 +4493,7 @@ def test_compose_w_delete_source_objects(self):
         source_1 = self._make_one(source_1_name, bucket=bucket)
         source_2 = self._make_one(source_2_name, bucket=bucket)
         destination = self._make_one(destination_name, bucket=bucket)
+        destination.content_type = content_type
 
         destination.compose(
             sources=[source_1, source_2],
@@ -4504,7 +4506,7 @@ def test_compose_w_delete_source_objects(self):
                 {"name": source_1.name, "generation": source_1.generation},
                 {"name": source_2.name, "generation": source_2.generation},
             ],
-            "destination": {},
+            "destination": {"contentType": content_type},
             "deleteSourceObjects": delete_source_objects,
         }
         expected_query_params = {}