Fatal error in exception handler on 405 HTML responses

Refiling. (The wscci component is vestigial.)

Also, RTBC. :-)

Let's get some tests for this.

+++ b/core/modules/system/lib/Drupal/system/Tests/System/ExceptionControllerTest.php
@@ -0,0 +1,37 @@
+  public function test405HTML() {
+    $exception_controller = new ExceptionController(new ContentNegotiation());
+    $response = $exception_controller->on405Html(new FlattenException(), new Request());
+    $this->assertEqual($response->getStatusCode(), 405, 'HTTP status of response is correct.');
+    $this->assertEqual($response->getContent(), 'Method Not Allowed', 'HTTP response body is correct.');
+  }

I'm unclear how this is testing the behavior of the request. We're directly calling an internal method, on405Html, which is too deep. That's an implementation detail. Rather, we need to call the actual controller method of ExceptionController() and confirm that we get back the correct Response object.

+++ b/core/modules/system/lib/Drupal/system/Tests/System/ExceptionControllerTest.php
@@ -0,0 +1,40 @@
+    $exception = new Exception('Test exception');

This needs to be new \Exception('Test exception').

In a namespaced file, classes sans-prefix are assumed to be in the current namespace if not "use"d. So PHP was converting "Exception" to "Drupal\system\Test\Exception, which of course doesn't exist.

Committed to 8.x. Will push at the end of my commit-spree.