add test case for fix#3 - `visited` flag results wrong toJSON outpul in event callback
add test case for fix#3 - `visited` flag results wrong toJSON outpul in event callback

Signed-off-by: Jaynti Kanani <54ef4d4ed0b9db4aaeba931a14be31b84d51ad24@gmail.com>

dhruvaray/backbone-associations