modules/test/CMakeLists.txt

@@ -4,4 +4,4 @@ add_library_module(fuzz_test test.cpp fuzz.cpp)
 target_link_libraries(test PUBLIC tbb logger)
 target_link_libraries(fuzz_test PUBLIC tbb logger)
 
-add_test_module(test test.test.cpp)
+add_test_module(test test.test.cpp mock.test.cpp)

modules/test/private/mock.test.cpp

@@ -0,0 +1,52 @@
+#include <test/mock.hpp>
+#include <test/test.hpp>
+
+using namespace lt::test;
+using namespace lt::test::mock;
+
+class ExpensiveClass
+{
+private:
+public:
+	virtual int expensive(std::string str, std::optional<int> opt)
+	{
+		return 0;
+	}
+};
+
+class MockClass: public ExpensiveClass
+{
+public:
+	int expensive(std::string str, std::optional<int> opt) override
+	{
+		return expensive_mock(str, opt);
+	};
+
+	Mock<int(std::string, std::optional<int>)> expensive_mock {};
+};
+
+class ExpensiveUser
+{
+public:
+	ExpensiveUser(ExpensiveClass &dependency)
+	{
+		dependency.expensive("", 10);
+	}
+};
+
+
+// problem #1: matcher functions should construct an invokable object to test against the indexed
+// argument.
+
+Suite raii = "mock_raii"_suite = [] {
+	Case { "happy path won't throw" } = [] {
+		auto a = std::function<int(int)> {};
+		auto expensive = MockClass {};
+		auto side_effect = false;
+		expensive.expensive_mock.expect("test", std::nullopt)
+		    .apply([&](auto str, auto opt) { side_effect = true; })
+		    .returns(69);
+
+		auto user = ExpensiveUser { expensive };
+	};
+};

modules/test/public/mock.hpp

@@ -0,0 +1,94 @@
+#pragma once
+
+namespace lt::test {
+
+template<typename _Signature>
+class Mock;
+
+template<typename Return_Type, typename... Arg_Types>
+class Mock<Return_Type(Arg_Types...)>
+{
+public:
+	auto at_least() -> Mock &
+	{
+		return *this;
+	}
+
+	auto operator&&(Mock &mock) -> Mock &
+	{
+		return mock;
+	}
+
+	auto operator()(Arg_Types... arguments) -> Return_Type
+	{
+		++m_call_index;
+
+		for (auto &side_effect : m_side_effects)
+		{
+			side_effect(std::forward<Arg_Types>(arguments)...);
+		}
+
+		if (m_return_func)
+		{
+			return m_return_func(std::forward<Arg_Types>(arguments)...);
+		}
+		return m_return_value;
+	}
+
+	/** With any arguments. */
+	template<uint32_t counter = 1>
+	auto expect() -> Mock &
+	{
+		m_expected_counter = counter;
+		return *this;
+	}
+
+	auto apply(std::function<void(Arg_Types...)> side_effect) -> Mock &
+	{
+		m_side_effects.emplace_back(std::move(side_effect));
+		return *this;
+	}
+
+	/** Returns a fixed value. */
+	auto returns(Return_Type value) -> Mock &
+	{
+		m_return_value = value;
+		return *this;
+	}
+
+	/** Returns a value based on input. */
+	auto returns(std::function<Return_Type(Arg_Types...)> func) -> Mock &
+	{
+		m_return_func = std::move(func);
+		return *this;
+	}
+
+private:
+	Return_Type m_return_value {};
+
+	std::function<Return_Type(Arg_Types...)> m_return_func {};
+
+	std::vector<std::function<void(Arg_Types...)>> m_side_effects {};
+
+	uint32_t m_call_index = 0;
+
+	std::vector<std::pair<std::tuple<Arg_Types...>, uint32_t>> m_expected_args;
+
+	uint32_t m_expected_counter {};
+};
+
+namespace mock::range {
+
+[[nodiscard]] auto is_empty() -> bool
+{
+	return false;
+}
+
+}; // namespace mock::range
+
+[[nodiscard]] auto eq(auto rhs) -> bool
+{
+	return false;
+}
+
+} // namespace lt::test