more tests and tweaks/fixes as a result

tests/test_local_function.cpp

@@ -0,0 +1,47 @@
+// Copyright (c) Lysann Tranvouez.  All rights reserved.
+
+#include <catch2/catch_test_macros.hpp>
+
+#include <mach_detours.h>
+
+static int localFunctionCounter = 0;
+int localFunction()
+{
+    localFunctionCounter++;
+    return 67;
+}
+int (*realLocalFunction)() = localFunction;
+static int localFunctionDetourCounter = 0;
+int localFunctionDetour()
+{
+    localFunctionDetourCounter++;
+    return 12;
+}
+
+TEST_CASE( "Overriding local function", "[local][attach]" )
+{
+    localFunctionCounter = 0;
+    localFunctionDetourCounter = 0;
+
+    CHECK( realLocalFunction == localFunction );
+    CHECK( localFunction() == 67 );
+    CHECK( localFunctionCounter == 1 );
+    CHECK( localFunctionDetourCounter == 0 );
+
+    CHECK( detour_transaction_begin() == err_none );
+    // Overriding a local function requires using detour_attach_and_commit instead of calling attach and commit individually.
+    // Otherwise when we return from attach (and before commit), the code page with the local function is marked as read+write (but _not_ executable).
+    // There is a good chance the code we return to (in this case the test function) is on the same memory page and can therefore not be executed (until we call commit).
+    CHECK( detour_attach_and_commit(reinterpret_cast<detour_func_t*>(&realLocalFunction), reinterpret_cast<detour_func_t>(localFunctionDetour)) == err_none );
+
+    CHECK( realLocalFunction != localFunction );
+    CHECK( localFunctionCounter == 1 );
+    CHECK( localFunctionDetourCounter == 0 );
+    CHECK( localFunction() == 12 );
+    CHECK( localFunctionCounter == 1 );
+    CHECK( localFunctionDetourCounter == 1 );
+
+    // clean up
+    CHECK( detour_transaction_begin() == err_none );
+    CHECK( detour_detach_and_commit(reinterpret_cast<detour_func_t*>(&realLocalFunction), reinterpret_cast<detour_func_t>(localFunctionDetour)) == err_none );
+}