Added tests for File Storage

[Pushkarm029]

part of #2

• currently, these tests are failing.

Tests Output :

running 1 test
thread 'tests::test_file_storage_integration' panicked at tests\integration_test.rs:33:9:
assertion `left == right` failed
  left: {"key2": "value2", "key1": "value1"}
 right: {}