Link substitution example for gtest

Author: PhysicsX

LinkTimeSubstitution/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.14)
+set(CMAKE_CXX_STANDARD 14)
+
+project(ExampleGtest LANGUAGES CXX)
+
+include(FetchContent)
+FetchContent_Declare(
+        googletest
+        GIT_REPOSITORY https://github.com/google/googletest.git
+        GIT_TAG        bf66935e07825318ae519675d73d0f3e313b3ec6 
+)
+FetchContent_MakeAvailable(googletest)
+
+add_executable(${PROJECT_NAME} example_test.cpp MockData.cpp)
+
+target_link_libraries(${PROJECT_NAME} gtest_main gmock_main)
+
+include(GoogleTest)
+gtest_discover_tests(${PROJECT_NAME})
+
+#include headers
+include_directories(include)

LinkTimeSubstitution/MockData.cpp

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+#include "Data.h"
+#include "MockData.h"
+#include <memory>
+
+MockData::Ptr global_mock_data_ptr = std::make_shared<MockData>();
+
+#include <iostream>
+int Data::call() {
+    std::cout<<__LINE__<<std::endl;
+    return global_mock_data_ptr->call();
+}

LinkTimeSubstitution/example.cpp

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+#include "Data.h"
+
+class Example {
+    Data data;
+
+public:
+    int foo() {
+        return data.call();
+    }
+};

LinkTimeSubstitution/example_test.cpp

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+#include <gtest/gtest.h>
+#include <gmock/gmock.h>
+#include "example.cpp"
+#include "MockData.h"
+
+extern std::shared_ptr<MockData> global_mock_data_ptr;
+
+class testFixture : public testing::Test
+{
+    public:
+    testFixture()
+    {
+    }
+    ~testFixture()
+    {
+        std::move(global_mock_data_ptr).reset(); // delete the global mock
+    }
+};
+
+
+TEST_F(testFixture, FooReturnsMockedValue) {
+
+    EXPECT_CALL(*global_mock_data_ptr, call()).WillOnce(::testing::Return(99));
+
+    Example ex; 
+    ASSERT_EQ(99, ex.foo());
+}

LinkTimeSubstitution/include/Data.h

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+#pragma once
+
+class Data {
+public:
+    virtual int call();
+    virtual ~Data() = default; // Add a virtual destructor for good measure
+
+};

LinkTimeSubstitution/include/MockData.h

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+#include "Data.h"
+#include <gmock/gmock.h>
+
+
+class MockData {
+public:
+    MOCK_METHOD(int, call, ());
+    using Ptr = std::shared_ptr<MockData>;
+};
+
+// Declare the global pointer to MockData
+extern MockData::Ptr global_mock_data_ptr;