fix(tests): proper handling of undefined literal value

New glimmer engines makes difference between null and undefined values. Note that previous behaviour
was an accident (cf. emberjs/ember.js#14016)
This commit updates tests to reflect that.
Was necessary to add conditional tests depending on the ember version. This version check relies on
the ``ember-version-is`` addon.

README.md

@@ -150,7 +150,22 @@ export default Ember.Route.extend({
 {{array-contains model 'Blacksad' property='title'}}
 ```
 
-Note that null or undefined are considered acceptable and equivalent values for 'value' parameter (resolve both to null)
+### ``null`` and ``undefined``
+
+``null`` and ``undefined`` are considered acceptable values for 'value' parameter.
+
+* **until ember 2.8**, ``null`` and ``undefined`` are both coerced to ``null`` by the templating engine. The following
+  expressions are therefore both leading to check for the presence of a ``null`` value inside the array:
+
+  ```hbs
+  {{array-contains collection null}}
+  {{array-contains collection undefined}}
+  ``` 
+
+* **ember 2.9 (glimmer)** changed this behaviour. ``undefined`` are then preserved and not coerced to ``null`` anymore.
+
+It could eventually break some apps relying on the initial behaviour but it has been considered as a fix since the first behaviour 
+was accidental. See [this issue](https://github.com/emberjs/ember.js/issues/14016) for details.
 
 ## Changelog
 

package.json

@@ -51,6 +51,7 @@
     "ember-paper": "1.0.0-alpha.3",
     "ember-resolver": "^2.0.3",
     "ember-runtime-enumerable-includes-polyfill": "^1.0.1",
+    "ember-version-is": "0.0.3",
     "loader.js": "^4.0.11",
     "urljs": "2.3.1",
     "yuidoc-ember-cli-theme": "Turbo87/yuidoc-ember-cli-theme"

tests/integration/helpers/array-contains-test.js

@@ -2,6 +2,10 @@ import Ember from 'ember';
 import { describeComponent, it } from 'ember-mocha';
 import { expect } from 'chai';
 import hbs from 'htmlbars-inline-precompile';
+import { is } from 'ember-version-is';
+
+// remove alpha, beta, canary, etc. suffixes to the current Ember version
+const BASE_VERSION =  Ember.VERSION.indexOf('-') === -1 ? Ember.VERSION : Ember.VERSION.substr(0, Ember.VERSION.indexOf('-'));
 
 describeComponent('array-contains', 'helper:array-contains', { integration: true }, function() {
 
@@ -25,6 +29,12 @@ describeComponent('array-contains', 'helper:array-contains', { integration: true
   it('should return true if literal contained', function () {
     this.set('array', ['c', 'string', 0, true, null]);
 
+    // before ember 2.9, null and undefined were both coerced to null
+    // (see https://github.com/emberjs/ember.js/issues/14016)
+    if (is(BASE_VERSION, "greaterThanOrEqualTo", "2.9.0")) {
+      this.get('array').push(undefined);
+    }
+
     this.render(hbs`{{array-contains array 'c'}}`);
     expect(this.$().text()).to.equal("true", "array should contain 'c'");
 
@@ -58,6 +68,13 @@ describeComponent('array-contains', 'helper:array-contains', { integration: true
 
     this.render(hbs`{{array-contains array false}}`);
     expect(this.$().text()).to.equal("false", "array should not contain 'false'");
+
+    // before ember 2.9, null and undefined were both coerced to null
+    // (see https://github.com/emberjs/ember.js/issues/14016)
+    if (is(BASE_VERSION, "greaterThanOrEqualTo", "2.9.0")) {
+      this.render(hbs`{{array-contains array undefined}}`);
+      expect(this.$().text()).to.equal("false", "array should not contain 'undefined'");
+    }
   });
 
   it('should return true if native object contained', function () {