diff --git a/internal/crosscompile/compile/rtlib/rt_test.go b/internal/crosscompile/compile/rtlib/rt_test.go
new file mode 100644
index 00000000..58aeb05e
--- /dev/null
+++ b/internal/crosscompile/compile/rtlib/rt_test.go
@@ -0,0 +1,124 @@
+package rtlib
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestPlatformSpecifiedFiles(t *testing.T) {
+	tests := []struct {
+		target   string
+		expected int // Number of expected files
+	}{
+		{"riscv32-unknown-elf", 5},
+		{"riscv64-unknown-elf", 27},
+		{"arm-none-eabi", 19},
+		{"avr-unknown-elf", 6},
+		{"xtensa", 2},
+		{"x86_64-pc-windows", 0},
+	}
+
+	builtinsDir := "/test/builtins"
+	for _, tt := range tests {
+		t.Run(tt.target, func(t *testing.T) {
+			result := platformSpecifiedFiles(builtinsDir, tt.target)
+			if len(result) != tt.expected {
+				t.Errorf("For target %s, expected %d files, got %d", tt.target, tt.expected, len(result))
+			}
+		})
+	}
+}
+
+func TestWithPlatformSpecifiedFiles(t *testing.T) {
+	baseDir := "/test/base"
+	target := "riscv32-unknown-elf"
+	inputFiles := []string{"file1.c", "file2.c"}
+
+	result := withPlatformSpecifiedFiles(baseDir, target, inputFiles)
+
+	// Should have input files + platform specific files
+	if len(result) <= len(inputFiles) {
+		t.Errorf("Expected more files than input, got %d", len(result))
+	}
+
+	// Check that input files are preserved
+	for _, inputFile := range inputFiles {
+		found := false
+		for _, resultFile := range result {
+			if resultFile == inputFile {
+				found = true
+				break
+			}
+		}
+		if !found {
+			t.Errorf("Input file %s not found in result", inputFile)
+		}
+	}
+}
+
+func TestGetCompilerRTConfig(t *testing.T) {
+	baseDir := "/test/base"
+	target := "riscv32-unknown-elf"
+
+	config := GetCompilerRTConfig(baseDir, target)
+
+	// Test groups configuration
+	if len(config.Groups) != 1 {
+		t.Errorf("Expected 1 group, got %d", len(config.Groups))
+	} else {
+		group := config.Groups[0]
+		expectedOutput := "libclang_builtins-" + target + ".a"
+		if group.OutputFileName != expectedOutput {
+			t.Errorf("Expected output file %s, got %s", expectedOutput, group.OutputFileName)
+		}
+
+		// Check that files list contains platform-specific files
+		if len(group.Files) == 0 {
+			t.Error("Expected non-empty files list")
+		}
+
+		// Check that CFlags are set
+		if len(group.CFlags) == 0 {
+			t.Error("Expected non-empty CFlags")
+		}
+
+		// Check that CCFlags are set
+		if len(group.CCFlags) == 0 {
+			t.Error("Expected non-empty CCFlags")
+		}
+	}
+}
+
+func TestGetCompilerRTConfig_DifferentTargets(t *testing.T) {
+	targets := []string{
+		"riscv32-unknown-elf",
+		"riscv64-unknown-elf",
+		"arm-none-eabi",
+		"avr-unknown-elf",
+		"xtensa",
+	}
+
+	baseDir := "/test/base"
+	for _, target := range targets {
+		t.Run(target, func(t *testing.T) {
+			config := GetCompilerRTConfig(baseDir, target)
+
+			// Basic validation
+			if config.Url == "" {
+				t.Error("URL should not be empty")
+			}
+			if config.ArchiveSrcDir == "" {
+				t.Error("ArchiveSrcDir should not be empty")
+			}
+			if len(config.Groups) == 0 {
+				t.Error("Should have at least one group")
+			}
+
+			// Check output filename contains target
+			group := config.Groups[0]
+			if !strings.Contains(group.OutputFileName, target) {
+				t.Errorf("Output filename %s should contain target %s", group.OutputFileName, target)
+			}
+		})
+	}
+}