diff --git a/source/network/tests/test_FSM.h b/source/network/tests/test_FSM.h
new file mode 100644
index 0000000000..eaae766394
--- /dev/null
+++ b/source/network/tests/test_FSM.h
@@ -0,0 +1,163 @@
+/* Copyright (C) 2023 Wildfire Games.
+ * This file is part of 0 A.D.
+ *
+ * 0 A.D. is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 0 A.D. is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "lib/self_test.h"
+
+#include "network/FSM.h"
+
+#include <array>
+
+class TestFSM : public CxxTest::TestSuite
+{
+	struct FSMGlobalState
+	{
+		std::array<size_t, 3> occurCount{0, 0, 0};
+	};
+
+	template<size_t N>
+	static bool editGlobal(void* state, const CFsmEvent*)
+	{
+		++std::get<N>(reinterpret_cast<FSMGlobalState*>(state)->occurCount);
+		return true;
+	}
+
+	static bool editParam(void*, CFsmEvent* event)
+	{
+		++*reinterpret_cast<size_t*>(event->GetParamRef());
+		return true;
+	}
+
+	enum class State : unsigned int
+	{
+		zero,
+		one,
+		two
+	};
+
+	enum class Instruction : unsigned int
+	{
+		toZero,
+		toOne,
+		toTwo
+	};
+
+public:
+
+	void test_global()
+	{
+		FSMGlobalState globalState;
+		CFsm FSMObject;
+
+		/*
+		Corresponding pseudocode
+
+		while (true)
+		{
+			// state zero
+			await nextInstruction();
+
+			// state one
+			const auto cond = await nextInstruction();
+
+			if (cond == instruction::toOne)
+			{
+				//state two
+				await nextInstruction();
+			}
+		}
+		*/
+
+		FSMObject.AddTransition(static_cast<unsigned int>(State::zero),
+			static_cast<unsigned int>(Instruction::toOne), static_cast<unsigned int>(State::one),
+			reinterpret_cast<void*>(&editGlobal<1>), static_cast<void*>(&globalState));
+		FSMObject.AddTransition(static_cast<unsigned int>(State::one),
+			static_cast<unsigned int>(Instruction::toTwo), static_cast<unsigned int>(State::two),
+			reinterpret_cast<void*>(&editGlobal<2>), static_cast<void*>(&globalState));
+		FSMObject.AddTransition(static_cast<unsigned int>(State::one),
+			static_cast<unsigned int>(Instruction::toZero), static_cast<unsigned int>(State::zero),
+			reinterpret_cast<void*>(&editGlobal<0>), static_cast<void*>(&globalState));
+		FSMObject.AddTransition(static_cast<unsigned int>(State::two),
+			static_cast<unsigned int>(Instruction::toZero), static_cast<unsigned int>(State::zero),
+			reinterpret_cast<void*>(&editGlobal<0>), static_cast<void*>(&globalState));
+
+		FSMObject.SetFirstState(static_cast<unsigned int>(State::zero));
+
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toOne), nullptr));
+		TS_ASSERT_EQUALS(std::get<1>(globalState.occurCount), 1);
+		TS_ASSERT_EQUALS(FSMObject.GetCurrState(), static_cast<unsigned int>(State::one));
+
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toTwo), nullptr));
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toZero), nullptr));
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toOne), nullptr));
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toZero), nullptr));
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toOne), nullptr));
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toZero), nullptr));
+		TS_ASSERT_EQUALS(std::get<0>(globalState.occurCount), 3);
+		TS_ASSERT_EQUALS(std::get<1>(globalState.occurCount), 3);
+		TS_ASSERT_EQUALS(std::get<2>(globalState.occurCount), 1);
+
+		// Some transitions do not exist.
+		TS_ASSERT(!FSMObject.Update(static_cast<unsigned int>(Instruction::toZero), nullptr));
+		TS_ASSERT(!FSMObject.Update(static_cast<unsigned int>(Instruction::toTwo), nullptr));
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toOne), nullptr));
+		TS_ASSERT(!FSMObject.Update(static_cast<unsigned int>(Instruction::toOne), nullptr));
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toTwo), nullptr));
+		TS_ASSERT(!FSMObject.Update(static_cast<unsigned int>(Instruction::toTwo), nullptr));
+		TS_ASSERT_EQUALS(std::get<0>(globalState.occurCount), 3);
+		TS_ASSERT_EQUALS(std::get<1>(globalState.occurCount), 4);
+		TS_ASSERT_EQUALS(std::get<2>(globalState.occurCount), 2);
+	}
+
+	void test_param()
+	{
+		FSMGlobalState globalState;
+		CFsm FSMObject;
+
+		// Equal to the FSM in test_global.
+		FSMObject.AddTransition(static_cast<unsigned int>(State::zero),
+			static_cast<unsigned int>(Instruction::toOne), static_cast<unsigned int>(State::one),
+			reinterpret_cast<void*>(&editParam), nullptr);
+		FSMObject.AddTransition(static_cast<unsigned int>(State::one),
+			static_cast<unsigned int>(Instruction::toTwo), static_cast<unsigned int>(State::two),
+			reinterpret_cast<void*>(&editParam), nullptr);
+		FSMObject.AddTransition(static_cast<unsigned int>(State::one),
+			static_cast<unsigned int>(Instruction::toZero), static_cast<unsigned int>(State::zero),
+			reinterpret_cast<void*>(&editParam), nullptr);
+		FSMObject.AddTransition(static_cast<unsigned int>(State::two),
+			static_cast<unsigned int>(Instruction::toZero), static_cast<unsigned int>(State::zero),
+			reinterpret_cast<void*>(&editParam), nullptr);
+
+		FSMObject.SetFirstState(static_cast<unsigned int>(State::zero));
+
+		// Some transitions do not exist.
+		TS_ASSERT(!FSMObject.Update(static_cast<unsigned int>(Instruction::toZero),
+			static_cast<void*>(&std::get<0>(globalState.occurCount))));
+		TS_ASSERT(!FSMObject.Update(static_cast<unsigned int>(Instruction::toTwo),
+			static_cast<void*>(&std::get<2>(globalState.occurCount))));
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toOne),
+			static_cast<void*>(&std::get<1>(globalState.occurCount))));
+		TS_ASSERT(!FSMObject.Update(static_cast<unsigned int>(Instruction::toOne),
+			static_cast<void*>(&std::get<1>(globalState.occurCount))));
+		TS_ASSERT(FSMObject.Update(static_cast<unsigned int>(Instruction::toTwo),
+			static_cast<void*>(&std::get<2>(globalState.occurCount))));
+		TS_ASSERT(!FSMObject.Update(static_cast<unsigned int>(Instruction::toTwo),
+			static_cast<void*>(&std::get<2>(globalState.occurCount))));
+		TS_ASSERT_EQUALS(std::get<0>(globalState.occurCount), 0);
+		TS_ASSERT_EQUALS(std::get<1>(globalState.occurCount), 1);
+		TS_ASSERT_EQUALS(std::get<2>(globalState.occurCount), 1);
+	}
+};