sem_open test cases make sure that it establish connection between the Semaphore and the process. There are checks for return values of the address, increament, decrement, and close. sem_open attempts to open an existing semaphore, which it should fail when both O_CREAT and O_EXCL name exist during the opening of a Semaphore. errno return EACCESS: sem_open exist and the permissions of Oflag are denied. errno return EEXIST: sem_open exist and O_CREAT and O_EXCL are set. errno return EINVAL: Create a semaphore with a value of SEM_VALUE_MAX. errno return ENOENT: O_CREAT is not set and the semaphore doesn't exist. errno return ENAMETOOLONG: This test case tries to creat a named semaphore that is longer than max limit. After sem_open() is called, the process can use the sem_t address returned to reference teh semaphore in calls to sem_wait(), sem_trywait(), sem_post(), and sem_close(). Until sem_close(), _exit(), or exec*() is called, the semaphore can be used in the process. If O_CREAT is set and a semaphore already exists, O_CREAT has no effect. If O_CREAT flag is used, sem_open has two additional args: mode_t which sets the permission bits and unsigned value which sets the initial value of the semaphore. The initial value for the semaphore should be less than or equal to SEM_VALUE_MAX. Any other initial value is invalid. The effective user ID of the process == the user ID of the semaphore. The system default group ID of the effective group ID of the process == the group ID of the semaphore. After sem_open has created semaphore "name", other process can use "name" to connect to that semaphore. If a process calls sem_open several times with the same name, the same adress must be returned as long as the semaphore has not been unlinked or closed as many times as opened.