test: support older Ember versions

Author: buschtoens

config/ember-try.js

@@ -21,6 +21,7 @@ module.exports = function() {
           npm: {
             devDependencies: {
               '@ember/jquery': '^0.5.1',
+              'ember-decorators-polyfill': '^1.0.5',
               'ember-source': '~2.18.0'
             }
           }
@@ -29,6 +30,7 @@ module.exports = function() {
           name: 'ember-lts-3.4',
           npm: {
             devDependencies: {
+              'ember-decorators-polyfill': '^1.0.5',
               'ember-source': '~3.4.0'
             }
           }
@@ -37,6 +39,7 @@ module.exports = function() {
           name: 'ember-lts-3.8',
           npm: {
             devDependencies: {
+              'ember-decorators-polyfill': '^1.0.5',
               'ember-source': '~3.8.0'
             }
           }

tests/unit/task-test.ts

@@ -1,5 +1,6 @@
 import { task, timeout } from 'ember-concurrency';
 import { module, test } from 'qunit';
+import { get } from '@ember/object';
 
 module('Unit | task', function() {
   test('simple task', async function(assert) {
@@ -14,7 +15,10 @@ module('Unit | task', function() {
       });
 
       async perform() {
-        const returnValue: 'foo' = await this.someTask.perform(1, 'foo');
+        const returnValue: 'foo' = await get(this, 'someTask').perform(
+          1,
+          'foo'
+        );
         assert.strictEqual(returnValue, 'foo');
       }
     }