Fail if expected exception was not thrown

src/Testing/GivenWhenThen/Scenario.php

@@ -170,6 +170,8 @@ public function assert(): self
             $handler = [$handler, 'handle'];
         }
 
+        $caughtException = false;
+
         try {
             ($handler)($instance->when->command);
         } catch (\Throwable $throwable) {
@@ -179,13 +181,19 @@ public function assert(): self
                 } else {
                     Assert::assertEquals($instance->expect, $throwable);
                 }
+
+                $caughtException = true;
             } else {
                 throw $throwable;
             }
         }
 
         $recordedEvents = $messageRepository->lastCommit();
 
+        if (isset($instance->expect) && !$caughtException) {
+            Assert::fail('Expected exception not thrown.');
+        }
+
         if (!isset($instance->outcome)) {
             Assert::fail('Expected an outcome.');
         }