c2b5aff446c719245e5451f24dc1cf01b1ad089c Issue #1934508-64: rename system.css_js_query_string to system.drupal_asset_query_string everywhere and add test for _drupal_flush_css_js().:
diff --git a/core/includes/common.inc b/core/includes/common.inc
index 349449a..8076ba8 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -4195,7 +4195,7 @@ function drupal_flush_all_caches() {
  */
 function _drupal_flush_css_js() {
   // The timestamp is converted to base 36 in order to make it more compact.
-  Drupal::state()->set('system.css_js_query_string', base_convert(REQUEST_TIME, 10, 36));
+  Drupal::state()->set('system.drupal_asset_query_string', base_convert(REQUEST_TIME, 10, 36));
 }
 
 /**
diff --git a/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php b/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
index 0d482fb..ef2d875 100644
--- a/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
+++ b/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
@@ -41,7 +41,7 @@ public function render(array $css_assets) {
     // browser-caching. The string changes on every update or full cache
     // flush, forcing browsers to load a new copy of the files, as the
     // URL changed.
-    $query_string = $this->state->get('system.css_js_query_string') ?: '0';
+    $query_string = $this->state->get('system.drupal_asset_query_string') ?: '0';
 
     // Defaults for LINK and STYLE elements.
     $link_element_defaults = array(
diff --git a/core/lib/Drupal/Core/Asset/JsCollectionRenderer.php b/core/lib/Drupal/Core/Asset/JsCollectionRenderer.php
index 807179f..c6db7a0 100644
--- a/core/lib/Drupal/Core/Asset/JsCollectionRenderer.php
+++ b/core/lib/Drupal/Core/Asset/JsCollectionRenderer.php
@@ -43,7 +43,7 @@ public function render(array $js_assets) {
     // URL changed. Files that should not be cached (see _drupal_add_js())
     // get REQUEST_TIME as query-string instead, to enforce reload on every
     // page request.
-    $default_query_string = $this->state->get('system.css_js_query_string') ?: '0';
+    $default_query_string = $this->state->get('system.drupal_asset_query_string') ?: '0';
 
     // For inline JavaScript to validate as XHTML, all JavaScript containing
     // XHTML needs to be wrapped in CDATA. To make that backwards compatible
diff --git a/core/modules/system/src/Tests/Common/CascadingStylesheetsTest.php b/core/modules/system/src/Tests/Common/CascadingStylesheetsTest.php
index 97b1fc6..84f5175 100644
--- a/core/modules/system/src/Tests/Common/CascadingStylesheetsTest.php
+++ b/core/modules/system/src/Tests/Common/CascadingStylesheetsTest.php
@@ -77,7 +77,7 @@ function testRenderFile() {
     $styles = drupal_get_css();
     $this->assertTrue(strpos($styles, $css) > 0, 'Rendered CSS includes the added stylesheet.');
     // Verify that newlines are properly added inside style tags.
-    $query_string = $this->container->get('state')->get('system.css_js_query_string') ?: '0';
+    $query_string = $this->container->get('state')->get('system.drupal_asset_query_string') ?: '0';
     $css_processed = '<link rel="stylesheet" href="' . check_plain(file_create_url($css)) . "?" . $query_string . '" media="all" />';
     $this->assertEqual(trim($styles), $css_processed, 'Rendered CSS includes newlines inside style tags for JavaScript use.');
   }
@@ -183,7 +183,7 @@ function testAddCssFileWithQueryString() {
     _drupal_add_css($css_with_query_string);
 
     $styles = drupal_get_css();
-    $query_string = $this->container->get('state')->get('system.css_js_query_string') ?: '0';
+    $query_string = $this->container->get('state')->get('system.drupal_asset_query_string') ?: '0';
     $this->assertTrue(strpos($styles, $css_without_query_string . '?' . $query_string), 'Query string was appended correctly to css.');
     $this->assertTrue(strpos($styles, str_replace('&', '&amp;', $css_with_query_string)), 'Query string not escaped on a URI.');
   }
diff --git a/core/modules/system/src/Tests/Common/JavaScriptTest.php b/core/modules/system/src/Tests/Common/JavaScriptTest.php
index f6f3da8..83b2985 100644
--- a/core/modules/system/src/Tests/Common/JavaScriptTest.php
+++ b/core/modules/system/src/Tests/Common/JavaScriptTest.php
@@ -108,7 +108,7 @@ function testAddExternal() {
    * Tests adding JavaScript files with additional attributes.
    */
   function testAttributes() {
-    $default_query_string = $this->container->get('state')->get('system.css_js_query_string') ?: '0';
+    $default_query_string = $this->container->get('state')->get('system.drupal_asset_query_string') ?: '0';
 
     $attached['#attached']['library'][] = 'core/drupal';
     $attached['#attached']['js']['http://example.com/script.js'] = array(
@@ -135,7 +135,7 @@ function testAggregatedAttributes() {
     // Enable aggregation.
     \Drupal::config('system.performance')->set('js.preprocess', 1)->save();
 
-    $default_query_string = $this->container->get('state')->get('system.css_js_query_string') ?: '0';
+    $default_query_string = $this->container->get('state')->get('system.drupal_asset_query_string') ?: '0';
 
     $attached['#attached']['library'][] = 'core/drupal';
     $attached['#attached']['js']['http://example.com/script.js'] = array(
@@ -353,7 +353,7 @@ function testDifferentWeight() {
    * @see drupal_pre_render_conditional_comments()
    */
   function testBrowserConditionalComments() {
-    $default_query_string = $this->container->get('state')->get('system.css_js_query_string') ?: '0';
+    $default_query_string = $this->container->get('state')->get('system.drupal_asset_query_string') ?: '0';
 
     $attached['#attached']['library'][] = 'core/drupal';
     $attached['#attached']['js']['core/misc/collapse.js'] = array(
@@ -390,7 +390,7 @@ function testVersionQueryString() {
    * Tests JavaScript grouping and aggregation.
    */
   function testAggregation() {
-    $default_query_string = $this->container->get('state')->get('system.css_js_query_string') ?: '0';
+    $default_query_string = $this->container->get('state')->get('system.drupal_asset_query_string') ?: '0';
 
     // To optimize aggregation, items with the 'every_page' option are ordered
     // ahead of ones without. The order of JavaScript execution must be the
@@ -700,7 +700,7 @@ function testAddJsFileWithQueryString() {
     $js = drupal_get_path('module', 'node') . '/node.js';
     _drupal_add_js($js);
 
-    $query_string = $this->container->get('state')->get('system.css_js_query_string') ?: '0';
+    $query_string = $this->container->get('state')->get('system.drupal_asset_query_string') ?: '0';
     $scripts = drupal_get_js();
     $this->assertTrue(strpos($scripts, $js . '?' . $query_string), 'Query string was appended correctly to JS.');
   }
diff --git a/core/modules/system/src/Tests/System/ThemeTest.php b/core/modules/system/src/Tests/System/ThemeTest.php
index ac62a72..0d63784 100644
--- a/core/modules/system/src/Tests/System/ThemeTest.php
+++ b/core/modules/system/src/Tests/System/ThemeTest.php
@@ -189,6 +189,39 @@ function testThemeSettings() {
   }
 
   /**
+   * Test clearing the Drupal asset query-string cache.
+   */
+  function testDrupalAssetCacheFlush() {
+
+    // Obtain the query-string.
+    try {
+      $query_string = \Drupal::state()->get('system.drupal_asset_query_string') ?: '0';
+    }
+    catch(Exception $e) {
+      $query_string = '0';
+    }
+
+    // Flush the query-string cache.
+    _drupal_flush_css_js();
+
+    // Obtain the new query-string.
+    try {
+      $new_query_string = \Drupal::state()->get('system.drupal_asset_query_string') ?: '0';
+    }
+    catch(Exception $e) {
+      $this->fail('Requesting Drupal asset query-string after cache flush produced an exception.');
+    }
+
+    // Ensure that a cache flush sets a non-zero query-string.
+    $this->assertNotIdentical($new_query_string, '0', 'Drupal asset query-string is non-zero after cache flush.');
+
+    // Ensure that a cache flush reset the query-string from its original value.
+    if ($new_query_string !== '0') {
+      $this->assertNotIdentical($query_string, $new_query_string, 'Drupal asset query-string changes after cache flush.');
+    }
+  }
+
+  /**
    * Test the administration theme functionality.
    */
   function testAdministrationTheme() {
diff --git a/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php b/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php
index 4184ec6..f5f8324 100644
--- a/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php
@@ -543,7 +543,7 @@ function providerTestRender() {
   function testRender(array $css_assets, array $render_elements) {
     $this->state->expects($this->once())
       ->method('get')
-      ->with('system.css_js_query_string')
+      ->with('system.drupal_asset_query_string')
       ->will($this->returnValue(NULL));
     $this->assertSame($render_elements, $this->renderer->render($css_assets));
   }
@@ -554,7 +554,7 @@ function testRender(array $css_assets, array $render_elements) {
   function testRenderInvalidType() {
     $this->state->expects($this->once())
       ->method('get')
-      ->with('system.css_js_query_string')
+      ->with('system.drupal_asset_query_string')
       ->will($this->returnValue(NULL));
     $this->setExpectedException('Exception', 'Invalid CSS asset type.');