func TestCorruptingMagicString(t *testing.T) {
	clear()
	u1, _ := InitUser("u1", "pass")
	u2, _ := InitUser("u2", "pass1")
	f1 := []byte("content")
	u1.StoreFile("f1", f1)
	access_token, err1 := u1.ShareFile("f1", "u2")
	if err1 != nil {
		t.Error("Couldn't share file")
		return
	}
	corrupt_token := access_token + "random_string"
	err2 := u2.ReceiveFile("newFile", "u1", corrupt_token)
	if err2 == nil {
		t.Error("Didn't detect corrupt access_token")
		return
	}
}