tests: Add basic error handling to callbacks, for reference

Many users look at both examples *and* unit tests to learn how to use a
library.  We should pride ourselves in that we have not just working but
also correct and readable tests.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

tests/timer.c

@@ -5,10 +5,13 @@
 #define TIMEOUT 2		/* 2 sec */
 struct timeval start;
 
-static void cb(uev_t *w, void *UNUSED(arg), int UNUSED(events))
+static void cb(uev_t *w, void *UNUSED(arg), int events)
 {
 	struct timeval now;
 
+	if (UEV_ERROR == events)
+		fprintf(stderr, "timer watcher failed, ignoring ...\n");
+
 	gettimeofday(&now, NULL);
 	fail_unless(now.tv_sec == start.tv_sec + TIMEOUT);