2 files changed, 22 insertions, 3 deletions
diff --git a/actionpack/test/dispatch/debug_exceptions_test.rb b/actionpack/test/dispatch/debug_exceptions_test.rb
index 5ae8a20ae4..3e57e8f4d9 100644
--- a/actionpack/test/dispatch/debug_exceptions_test.rb
+++ b/actionpack/test/dispatch/debug_exceptions_test.rb
@@ -620,4 +620,23 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
       assert_select 'input[value="Action 2"]'
     end
   end
+
+  test "debug exceptions app shows diagnostics when malformed query parameters are provided" do
+    @app = DevelopmentApp
+
+    get "/bad_request?x[y]=1&x[y][][w]=2"
+
+    assert_response 400
+    assert_match "ActionController::BadRequest", body
+  end
+
+  test "debug exceptions app shows diagnostics when malformed query parameters are provided by XHR" do
+    @app = DevelopmentApp
+    xhr_request_env = { "action_dispatch.show_exceptions" => true, "HTTP_X_REQUESTED_WITH" => "XMLHttpRequest" }
+
+    get "/bad_request?x[y]=1&x[y][][w]=2", headers: xhr_request_env
+
+    assert_response 400
+    assert_match "ActionController::BadRequest", body
+  end
 end
diff --git a/actionpack/test/dispatch/middleware_stack_test.rb b/actionpack/test/dispatch/middleware_stack_test.rb
index 90f2eccd19..c534e60c74 100644
--- a/actionpack/test/dispatch/middleware_stack_test.rb
+++ b/actionpack/test/dispatch/middleware_stack_test.rb
@@ -121,9 +121,6 @@ class MiddlewareStackTest < ActiveSupport::TestCase
   end
 
   test "instruments the execution of middlewares" do
-    app = @stack.build(proc { |env| [200, {}, []] })
-    env = {}
-
     events = []
 
     subscriber = proc do |*args|
@@ -131,6 +128,9 @@ class MiddlewareStackTest < ActiveSupport::TestCase
     end
 
     ActiveSupport::Notifications.subscribed(subscriber, "process_middleware.action_dispatch") do
+      app = @stack.build(proc { |env| [200, {}, []] })
+
+      env = {}
       app.call(env)
     end