Update to Drupal 8.2.0. For more information, see https://www.drupal.org/project/drupal/releases/8.2.0

core/tests/Drupal/Tests/Component/Render/FormattableMarkupTest.php

@@ -13,6 +13,20 @@ use Drupal\Tests\UnitTestCase;
  */
 class FormattableMarkupTest extends UnitTestCase {
 
+  /**
+   * The error message of the last error in the error handler.
+   *
+   * @var string
+   */
+  protected $lastErrorMessage;
+
+  /**
+   * The error number of the last error in the error handler.
+   *
+   * @var int
+   */
+  protected $lastErrorNumber;
+
   /**
    * @covers ::__toString
    * @covers ::jsonSerialize
@@ -35,4 +49,54 @@ class FormattableMarkupTest extends UnitTestCase {
     $this->assertEquals(strlen($string), $formattable_string->count());
   }
 
+  /**
+   * Custom error handler that saves the last error.
+   *
+   * We need this custom error handler because we cannot rely on the error to
+   * exception conversion as __toString is never allowed to leak any kind of
+   * exception.
+   *
+   * @param int $error_number
+   *   The error number.
+   * @param string $error_message
+   *   The error message.
+   */
+  public function errorHandler($error_number, $error_message) {
+    $this->lastErrorNumber = $error_number;
+    $this->lastErrorMessage = $error_message;
+  }
+
+  /**
+   * @covers ::__toString
+   * @dataProvider providerTestUnexpectedPlaceholder
+   */
+  public function testUnexpectedPlaceholder($string, $arguments, $error_number, $error_message) {
+    // We set a custom error handler because of https://github.com/sebastianbergmann/phpunit/issues/487
+    set_error_handler([$this, 'errorHandler']);
+    // We want this to trigger an error.
+    $markup = new FormattableMarkup($string, $arguments);
+    // Cast it to a string which will generate the errors.
+    $output = (string) $markup;
+    restore_error_handler();
+    // The string should not change.
+    $this->assertEquals($string, $output);
+    $this->assertEquals($error_number, $this->lastErrorNumber);
+    $this->assertEquals($error_message, $this->lastErrorMessage);
+  }
+
+  /**
+   * Data provider for FormattableMarkupTest::testUnexpectedPlaceholder().
+   *
+   * @return array
+   */
+  public function providerTestUnexpectedPlaceholder() {
+    return [
+      ['Non alpha starting character: ~placeholder', ['~placeholder' => 'replaced'], E_USER_ERROR, 'Invalid placeholder (~placeholder) in string: Non alpha starting character: ~placeholder'],
+      ['Alpha starting character: placeholder', ['placeholder' => 'replaced'], E_USER_DEPRECATED, 'Invalid placeholder (placeholder) in string: Alpha starting character: placeholder'],
+      // Ensure that where the placeholder is located in the the string is
+      // irrelevant.
+      ['placeholder', ['placeholder' => 'replaced'], E_USER_DEPRECATED, 'Invalid placeholder (placeholder) in string: placeholder'],
+    ];
+  }
+
 }