Test store remains open until last reference is closed.

Author: greenrobot-team

objectbox/test/basics_test.dart

@@ -70,10 +70,14 @@ void main() {
 
     final id = store1.box<TestEntity>().put(TestEntity(tString: 'foo'));
     expect(id, 1);
+    // Close original store to test store remains open until all refs closed.
+    store1.close();
+    expect(true, Store.isOpen('testdata-basics'));
     final read = store2.box<TestEntity>().get(id);
     expect(read, isNotNull);
     expect(read!.tString, 'foo');
     store2.close();
+    expect(false, Store.isOpen('testdata-basics'));
     env.closeAndDelete();
   });