Ensure that PHPUnit's error handler is still working in isolated tests

Author: alexpott

src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler.php

@@ -255,6 +255,12 @@ public static function collectDeprecations($outputFile)
             }
             $deprecations[] = array(error_reporting(), $msg);
         });
+        // This can be registered before the PHPUnit error handler.
+        if (!$previousErrorHandler) {
+            $UtilPrefix = class_exists('PHPUnit_Util_ErrorHandler') ? 'PHPUnit_Util_' : 'PHPUnit\Util\\';
+            $previousErrorHandler = $UtilPrefix.'ErrorHandler::handleError';
+        }
+
         register_shutdown_function(function () use ($outputFile, &$deprecations) {
             file_put_contents($outputFile, serialize($deprecations));
         });

src/Symfony/Bridge/PhpUnit/Tests/ProcessIsolationTest.php

@@ -21,4 +21,17 @@ public function testIsolation()
         @trigger_error('Test abc', E_USER_DEPRECATED);
         $this->addToAssertionCount(1);
     }
+
+    public function testCallingOtherErrorHandler()
+    {
+        $class = class_exists('PHPUnit\Framework\Exception') ? 'PHPUnit\Framework\Exception' : 'PHPUnit_Framework_Exception';
+        if (method_exists($this, 'expectException')) {
+            $this->expectException($class);
+            $this->expectExceptionMessage('Test that PHPUnit\'s error handler fires.');
+        } else {
+            $this->setExpectedException($class, 'Test that PHPUnit\'s error handler fires.');
+        }
+
+        trigger_error('Test that PHPUnit\'s error handler fires.', E_USER_WARNING);
+    }
 }