test: make status test more robust

Rework assertions to report helpful messages on failure.

Increase the "elapsed" limit from 100ms to 300ms to support our
slow CI machines.

test/app.test.js

@@ -12,6 +12,7 @@ var loopback = require('../');
 var PersistedModel = loopback.PersistedModel;
 
 var describe = require('./util/describe');
+var expect = require('chai').expect;
 var it = require('./util/it');
 
 describe('app', function() {
@@ -937,18 +938,14 @@ describe('app', function() {
         .end(function(err, res) {
           if (err) return done(err);
 
-          assert.equal(typeof res.body, 'object');
+          expect(res.body).to.be.an('object');
-          assert(res.body.started);
+          expect(res.body).to.have.property('started');
-          // The number can be 0
+          expect(res.body.uptime, 'uptime').to.be.gte(0);
-          assert(res.body.uptime !== undefined);
 
           var elapsed = Date.now() - Number(new Date(res.body.started));
 
-          // elapsed should be a positive number...
+          // elapsed should be a small positive number...
-          assert(elapsed >= 0);
+          expect(elapsed, 'elapsed').to.be.within(0, 300);
-
-          // less than 100 milliseconds
-          assert(elapsed < 100);
 
           done();
         });