Update tag for preview cache (ezsystems#153)

* Update tag for purging preview cache

The admin preview function does not display the draft content that is
currently being edited, this is because the preview cache is not purged,
and the preview function always fetches content from the view cache,
refer to ezsystems/ezpublish-kernel#2396 for details.

To fix this issue, `PersistenceCachePurger.php::contentVersion()` has
been changed to invalidate cache with the new tags.

| Question           | Answer
| ------------------ | ------------------
| **JIRA issue**     | n/a
| **Bug**            | yes
| **New feature**    | no
| **Target version** | `v2.0.0`
| **BC breaks**      | no
| **Tests pass**     | yes
| **Doc needed**     | no

**TODO**:
- [ ] Implement feature / fix a bug.
- [ ] Implement tests.
- [ ] Fix new code according to Coding Standards (`$ composer fix-cs`).
- [x] Ask for Code Review.

* Update PersistenceCachePurger.php

* Update PersistenceCachePurgerTest.php

bundle/Cache/PersistenceCachePurger.php

@@ -167,8 +167,9 @@ public function contentVersion($contentId, $versionNo)
             return;
         }
 
+        // todo Once we can require 2.2.2+, simplify to just invalidate "content-{$contentId}-version-{$versionNo}"
         $this->cache->deleteItem("ez-content-version-info-${contentId}-${versionNo}");
-        $this->cache->invalidateTags(["content-${contentId}-version-list"]);
+        $this->cache->invalidateTags(["content-${contentId}-version-list", "content-{$contentId}-version-{$versionNo}"]);
     }
 
     /**

bundle/Tests/Cache/PersistenceCachePurgerTest.php

@@ -389,4 +389,30 @@ public function testClearUserFail()
     {
         $this->cachePurger->user(new \stdClass());
     }
+
+    /**
+     * @covers \eZ\Bundle\EzPublishLegacyBundle\Cache\PersistenceCachePurger::contentVersion
+     * @dataProvider getDataForTestClearVersionForOneContent
+     */
+    public function testClearVersionOfOneContent($contentId, $versionNo)
+    {
+        $this->cacheService
+            ->expects($this->once())
+            ->method('deleteItem')
+            ->with("ez-content-version-info-${contentId}-${versionNo}");
+
+        $this->cacheService
+            ->expects($this->once())
+            ->method('invalidateTags')
+            ->with(["content-${contentId}-version-list", "content-${contentId}-version-${versionNo}"]);
+
+        $this->cachePurger->contentVersion($contentId, $versionNo);
+    }
+
+    public function getDataForTestClearVersionForOneContent()
+    {
+        return [
+            [18, 37],
+        ];
+    }
 }