Issue #2492429 by mikeryan: Migration count caching broken

core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php

@@ -423,7 +423,7 @@ abstract class SourcePluginBase extends PluginBase implements MigrateSourceInter
     // class to get the count from the source.
     if ($refresh || !$this->cacheCounts) {
       $count = $this->getIterator()->count();
-      $this->getCache()->set($this->cacheKey, $count, 'cache');
+      $this->getCache()->set($this->cacheKey, $count);
     }
     else {
       // Caching is in play, first try to retrieve a cached count.
@@ -436,7 +436,7 @@ abstract class SourcePluginBase extends PluginBase implements MigrateSourceInter
         // No cached count, ask the derived class to count 'em up, and cache
         // the result.
         $count = $this->getIterator()->count();
-        $this->getCache()->set($this->cacheKey, $count, 'cache');
+        $this->getCache()->set($this->cacheKey, $count);
       }
     }
     return $count;

core/modules/migrate/tests/src/Unit/MigrateSourceTest.php

@@ -139,10 +139,12 @@ class MigrateSourceTest extends MigrateTestCase {
    * Test that the source count is correct.
    */
   public function testCount() {
-
+    // Use the Apcu cache backend, which confirms that the cache API is being
+    // properly used.
     $container = new ContainerBuilder();
-    $container->register('cache.migrate', 'Drupal\Core\Cache\NullBackend')
-      ->setArguments(['migrate']);
+    $cache_tags_checksum = $this->getMock('\Drupal\Core\Cache\CacheTagsChecksumInterface');
+    $container->register('cache.migrate', 'Drupal\Core\Cache\ApcuBackend')
+      ->setArguments(['migrate', 'migrate', $cache_tags_checksum]);
     \Drupal::setContainer($container);
 
     // Test that the basic count works.