Problem: intermittent timeouts on test_heartbeats

Solution: increase number of retries when reading monitor event,
and increase timeout

tests/test_heartbeats.cpp

@@ -50,7 +50,7 @@ SETUP_TEARDOWN_TESTCONTEXT
 
 static int get_monitor_event (void *monitor_)
 {
-    for (int i = 0; i < 2; i++) {
+    for (int i = 0; i < 10; i++) {
         //  First frame in message contains event number and value
         zmq_msg_t msg;
         TEST_ASSERT_SUCCESS_ERRNO (zmq_msg_init (&msg));
@@ -417,7 +417,9 @@ void test_setsockopt_heartbeat_ttl_near_zero ()
 
 int main (void)
 {
-    setup_test_environment ();
+    //  The test cases are very long-running. The default timeout of 60 seconds
+    //  is not always enough.
+    setup_test_environment (90);
 
     UNITY_BEGIN ();