add test case

tests/CMakeLists.txt

@@ -1,6 +1,14 @@
 add_executable(mach_detours_tests
         test.cpp)
 
+add_library(mach_detours_test_func SHARED
+        test_func.c
+        test_func.h
+)
+
 target_link_libraries(mach_detours_tests
-        PRIVATE Catch2::Catch2WithMain mach_detours
+        PRIVATE
+            mach_detours
+            Catch2::Catch2WithMain
+            mach_detours_test_func
 )

tests/test.cpp

@@ -1 +1,37 @@
 // Copyright (c) Lysann Tranvouez.  All rights reserved.
+
+#include <catch2/catch_test_macros.hpp>
+
+#include <mach_detours.h>
+
+#include "test_func.h"
+
+static int testFunctionDetourCounter = 0;
+int testFunctionDetour()
+{
+    testFunctionDetourCounter++;
+    return 94;
+}
+
+TEST_CASE( "Overriding custom function" )
+{
+    int (*realTestFunction)() = testFunction;
+    testFunctionCounter = 0;
+    testFunctionDetourCounter = 0;
+
+    REQUIRE( testFunction() == 42 );
+    REQUIRE( testFunctionCounter == 1 );
+    REQUIRE( testFunctionDetourCounter == 0 );
+
+    CHECK( detour_transaction_begin() == err_none );
+    CHECK( detour_attach(reinterpret_cast<detour_func_t*>(&realTestFunction), reinterpret_cast<detour_func_t>(testFunctionDetour)) == err_none );
+    CHECK( detour_transaction_commit() == err_none );
+
+    REQUIRE( realTestFunction != testFunction );
+
+    REQUIRE( testFunctionCounter == 1 );
+    REQUIRE( testFunctionDetourCounter == 0 );
+    REQUIRE( testFunction() == 94 );
+    REQUIRE( testFunctionCounter == 1 );
+    REQUIRE( testFunctionDetourCounter == 1 );
+}

tests/test_func.c

@@ -0,0 +1,9 @@
+#include "test_func.h"
+
+int testFunctionCounter = 0;
+
+int testFunction()
+{
+    testFunctionCounter++;
+    return 42;
+}

tests/test_func.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern int testFunctionCounter;
+
+int testFunction();
+
+#ifdef __cplusplus
+}
+#endif