[wpilib] Throw early when EventLoop is modified while running (#6115)

wpilibc/src/test/native/cpp/event/EventLoopTest.cpp

@@ -0,0 +1,24 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include <gtest/gtest.h>
+
+#include "frc/Errors.h"
+#include "frc/event/EventLoop.h"
+
+using namespace frc;
+
+TEST(EventLoopTest, ConcurrentModification) {
+  EventLoop loop;
+
+  loop.Bind([&loop] { ASSERT_THROW(loop.Bind([] {}), frc::RuntimeError); });
+
+  loop.Poll();
+
+  loop.Clear();
+
+  loop.Bind([&loop] { ASSERT_THROW(loop.Clear(), frc::RuntimeError); });
+
+  loop.Poll();
+}