Small refactoring with minor improvements.

tests/test_repository.py

@@ -49,7 +49,7 @@ def test_read_write_blob(tmp_dir: Path, repo: Repository):
         digest = repo.add_blob(stream)
 
     blob = repo.get_blob(digest)
-    data = blob.read()
+    data = blob.reader().read()
 
     with path.open("rb") as stream:
         assert data == stream.read()

tests/test_simple_cas.py

@@ -55,7 +55,9 @@ def test_simple_cas(tmp_dir: Path):
 
         obj = cas.read(digest)
         assert obj is not None
+        assert obj.digest == digest
         assert obj.object_type == b"blob"
+        assert obj.size == len(data)
         assert obj.data == data
 
     cas = SimpleCas(
@@ -68,7 +70,9 @@ def test_simple_cas(tmp_dir: Path):
 
         obj = cas.read(digest)
         assert obj is not None
+        assert obj.digest == digest
         assert obj.object_type == b"blob"
+        assert obj.size == len(data)
         assert obj.data == data
 
         digest2 = cas.write(b"blob", data)