Add test that verifies the hibernation detection behaviour

The real-world test would be to actually wait for a couple of minutes (with 2 *
heartbeat of default settings) in the unit test, but this is not feasible, so
just modify the heartbeat-setting to a lower value.

I tested it by only running tests inside `tests/timeago.test.js` and by actually
deploying this code and testing the alarms with Pushover and reading the logs in
Papertrail.

Before this change, I saw a 'Hibernation detected' log every minute. After this
change, I didn't see it anymore, probably because the app wasn't actually
hibernated (yet).

tests/timeago.test.js

@@ -7,6 +7,8 @@ describe('timeago', function() {
   ctx.ddata = require('../lib/data/ddata')();
   ctx.notifications = require('../lib/notifications')(env, ctx);
   ctx.language = require('../lib/language')();
+  ctx.settings = require('../lib/settings')();
+  ctx.settings.heartbeat = 0.5; // short heartbeat to speedup tests
 
   var timeago = require('../lib/plugins/timeago')(ctx);
 
@@ -41,6 +43,32 @@ describe('timeago', function() {
     done();
   });
 
+  it('should suspend alarms due to hibernation when 2 heartbeats are skipped', function() {
+    ctx.ddata.sgvs = [{ mills: Date.now() - times.mins(16).msecs, mgdl: 100, type: 'sgv' }];
+
+    var sbx = freshSBX()
+    var status = timeago.checkStatus(sbx);
+    // By default (no hibernation detected) a warning should be given
+    should.equal(status, 'warn')
+
+    // 10ms more than suspend-threshold to prevent flapping tests
+    var timeoutMs = 2 * ctx.settings.heartbeat * 1000 + 100;
+    return new Promise(function(resolve, reject) {
+      setTimeout(function() {
+        status = timeago.checkStatus(sbx);
+        // Because hibernation should now be detected, no warning should be given
+        should.equal(status, 'current')
+
+        // We immediately ask status again, so hibernation should not be detected anymore,
+        // and we should receive a warning again
+        status = timeago.checkStatus(sbx);
+        should.equal(status, 'warn')
+
+        resolve()
+      }, timeoutMs)
+    })
+  });
+
   it('should trigger a warning when data older than 15m', function(done) {
     ctx.notifications.initRequests();
     ctx.ddata.sgvs = [{ mills: Date.now() - times.mins(16).msecs, mgdl: 100, type: 'sgv' }];