diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 03572a6..bedf474 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -344,7 +344,7 @@ function t($string, array $args = array(), array $options = array()) {
  * @see t()
  * @ingroup sanitization
  */
-function format_string($string, array $args = array()) {
+function format_string($string, array $args) {
   return SafeMarkup::format($string, $args);
 }
 
diff --git a/core/modules/config/src/Tests/ConfigFileContentTest.php b/core/modules/config/src/Tests/ConfigFileContentTest.php
index 1347db5..8818f41 100644
--- a/core/modules/config/src/Tests/ConfigFileContentTest.php
+++ b/core/modules/config/src/Tests/ConfigFileContentTest.php
@@ -121,16 +121,16 @@ function testReadWriteConfig() {
     $this->assertNull($config->get('i.dont.exist'), 'Non-existent nested value returned NULL.');
 
     // Read false value.
-    $this->assertEqual($config->get($false_key), '0', format_string("Boolean FALSE value returned the string '0'."));
+    $this->assertEqual($config->get($false_key), '0', "Boolean FALSE value returned the string '0'.");
 
     // Read true value.
-    $this->assertEqual($config->get($true_key), '1', format_string("Boolean TRUE value returned the string '1'."));
+    $this->assertEqual($config->get($true_key), '1', "Boolean TRUE value returned the string '1'.");
 
     // Read null value.
     $this->assertIdentical($config->get('null'), NULL);
 
     // Read false that had been nested in an array value.
-    $this->assertEqual($config->get($casting_array_false_value_key), '0', format_string("Nested boolean FALSE value returned the string '0'."));
+    $this->assertEqual($config->get($casting_array_false_value_key), '0', "Nested boolean FALSE value returned the string '0'.");
 
     // Unset a top level value.
     $config->clear($key);
diff --git a/core/modules/field/src/Tests/String/RawStringFormatterTest.php b/core/modules/field/src/Tests/String/RawStringFormatterTest.php
index 020a2e3..82f6973 100644
--- a/core/modules/field/src/Tests/String/RawStringFormatterTest.php
+++ b/core/modules/field/src/Tests/String/RawStringFormatterTest.php
@@ -123,7 +123,7 @@ public function testStringFormatter() {
 
     // Verify the cache tags.
     $build = $entity->{$this->fieldName}->view();
-    $this->assertTrue(!isset($build[0]['#cache']), format_string('The string formatter has no cache tags.'));
+    $this->assertTrue(!isset($build[0]['#cache']), 'The string formatter has no cache tags.');
   }
 
 }
diff --git a/core/modules/field/src/Tests/String/StringFormatterTest.php b/core/modules/field/src/Tests/String/StringFormatterTest.php
index 4af818e..dcb515e 100644
--- a/core/modules/field/src/Tests/String/StringFormatterTest.php
+++ b/core/modules/field/src/Tests/String/StringFormatterTest.php
@@ -123,7 +123,7 @@ public function testStringFormatter() {
 
     // Verify the cache tags.
     $build = $entity->{$this->fieldName}->view();
-    $this->assertTrue(!isset($build[0]['#cache']), format_string('The string formatter has no cache tags.'));
+    $this->assertTrue(!isset($build[0]['#cache']), 'The string formatter has no cache tags.');
 
     $value = $this->randomMachineName();
     $entity->{$this->fieldName}->value = $value;
diff --git a/core/modules/system/src/Tests/Ajax/FrameworkTest.php b/core/modules/system/src/Tests/Ajax/FrameworkTest.php
index c7ccd8b..6ab1c5e 100644
--- a/core/modules/system/src/Tests/Ajax/FrameworkTest.php
+++ b/core/modules/system/src/Tests/Ajax/FrameworkTest.php
@@ -165,7 +165,7 @@ public function testLazyLoad() {
     // the first AJAX command.
     $this->assertIdentical($new_settings[$expected['setting_name']], $expected['setting_value'], format_string('Page now has the %setting.', array('%setting' => $expected['setting_name'])));
     $expected_command = new SettingsCommand(array($expected['setting_name'] => $expected['setting_value']), TRUE);
-    $this->assertCommand(array_slice($commands, 0, 1), $expected_command->render(), format_string('The settings command was first.'));
+    $this->assertCommand(array_slice($commands, 0, 1), $expected_command->render(), 'The settings command was first.');
 
     // Verify the expected CSS file was added, both to drupalSettings, and as
     // the second AJAX command for inclusion into the HTML.
diff --git a/core/modules/system/src/Tests/Entity/EntityQueryTest.php b/core/modules/system/src/Tests/Entity/EntityQueryTest.php
index fd4165b..4130804 100644
--- a/core/modules/system/src/Tests/Entity/EntityQueryTest.php
+++ b/core/modules/system/src/Tests/Entity/EntityQueryTest.php
@@ -554,7 +554,7 @@ protected function assertBundleOrder($order) {
           }
         }
       }
-      $this->assertTrue($ok, format_string("$i is after all entities in bundle2"));
+      $this->assertTrue($ok, "$i is after all entities in bundle2");
     }
   }
 
diff --git a/core/modules/system/src/Tests/Path/AliasTest.php b/core/modules/system/src/Tests/Path/AliasTest.php
index 4281905..2ceb4c9 100644
--- a/core/modules/system/src/Tests/Path/AliasTest.php
+++ b/core/modules/system/src/Tests/Path/AliasTest.php
@@ -52,7 +52,7 @@ function testCRUD() {
 
     // Load alias by source path.
     $loadedAlias = $aliasStorage->load(array('source' => '/node/1'));
-    $this->assertEqual($loadedAlias['alias'], '/alias_for_node_1_und', format_string('The last created alias loaded by default.'));
+    $this->assertEqual($loadedAlias['alias'], '/alias_for_node_1_und', 'The last created alias loaded by default.');
 
     //Update a few aliases
     foreach ($aliases as $alias) {