[tests] Add edge case coverage for CopyIncludePaths in Paths.cpp

unittests/CppInterOp/CMakeLists.txt

@@ -21,6 +21,7 @@ add_cppinterop_unittest(CppInterOpTests
   TypeReflectionTest.cpp
   Utils.cpp
   VariableReflectionTest.cpp
+  PathsTest.cpp
   ${EXTRA_TEST_SOURCE_FILES}
 )
 

unittests/CppInterOp/PathsTest.cpp

@@ -0,0 +1,40 @@
+#include "gtest/gtest.h"
+#include "clang/Lex/HeaderSearchOptions.h"
+#include "llvm/ADT/SmallVector.h"
+#include <string>
+#include <algorithm>
+#include <string>
+
+
+#include "../../lib/CppInterOp/Paths.h" 
+
+namespace {
+
+TEST(PathsTest, CopyIncludePathsEdgeCases) {
+    clang::HeaderSearchOptions Opts;
+
+    // Set up edge-case flags to trigger uncovered branches
+    Opts.ModuleCachePath = "/tmp/fake_cache"; // Triggers -fmodule-cache-path
+    Opts.UseStandardSystemIncludes = false;   // Triggers -nostdinc
+    Opts.UseStandardCXXIncludes = false;      // Triggers -nostdinc++
+    Opts.UseLibcxx = true;                    // Triggers -stdlib=libc++
+    Opts.Verbose = true;                      // Triggers -v
+
+    llvm::SmallVector<std::string, 16> IncPaths;
+
+    CppInternal::utils::CopyIncludePaths(Opts, IncPaths, true, true);
+
+    auto Contains = [&](const std::string& flag) {
+        return std::find(IncPaths.begin(), IncPaths.end(), flag) != IncPaths.end();
+    };
+
+    // Verify the results
+    EXPECT_TRUE(Contains("-fmodule-cache-path"));
+    EXPECT_TRUE(Contains("/tmp/fake_cache"));
+    EXPECT_TRUE(Contains("-nostdinc"));
+    EXPECT_TRUE(Contains("-nostdinc++"));
+    EXPECT_TRUE(Contains("-stdlib=libc++"));
+    EXPECT_TRUE(Contains("-v"));
+}
+
+} // end anonymous namespace