reject with useful reason, rather then undefined when a scheduled fet…

…ch fails to contain an expected record.

addon/-private/system/store.js

@@ -906,10 +906,11 @@ Store = Service.extend({
 
     function rejectInternalModels(internalModels, error) {
       for (let i = 0, l = internalModels.length; i < l; i++) {
-        let pair = seeking[internalModels[i].id];
+        let internalModel = internalModels[i];
+        let pair = seeking[internalModel.id];
 
         if (pair) {
-          pair.resolver.reject(error);
+          pair.resolver.reject(error || new Error(`Expected: '${internalModel}' to be present in the adapter provided payload, but it was not found.`));
         }
       }
     }

tests/integration/adapter/rest-adapter-test.js

@@ -1947,10 +1947,10 @@ testInDebug('coalesceFindRequests assert.warns if the expected records are not r
   adapter.coalesceFindRequests = true;
 
   ajaxResponse({ comments: [{ id: 1 }] });
-  var post;
 
-  assert.expectWarning(function() {
-    run(function() {
+  let wait;
+  assert.expectWarning(() => {
+    run(() => {
       store.push({
         data: {
           type: 'post',
@@ -1967,9 +1967,13 @@ testInDebug('coalesceFindRequests assert.warns if the expected records are not r
         }
       });
 
-      post = store.peekRecord('post', 2);
-      post.get('comments');
+      let post = store.peekRecord('post', 2);
+      wait = post.get('comments').catch(e => {
+        assert.equal(e.message, `Expected: '<comment:2>' to be present in the adapter provided payload, but it was not found.`)
+      })
     });
+
+    return wait;
   }, /expected to find records with the following ids in the adapter response but they were missing: \[2,3\]/);
 });