This document defines the coverage for the pthread_mutex_trylock function:

Assertion	Tested?
1		YES
2		NO   * PTHREAD_MUTEX_RECURSIVE is a new XSI feature, which may not
		       be available in pthread implementations
3		YES
4		YES  * EINVAL and EAGAIN are relevant to low-priority mutex
		       attributes, which cannot be tested by now
		     * When it specifies it 'may' fail and not 'shall' fail,
		       it will always return PASS, but will return a
		       PASS and print out a warning if it fails.
NOTE: