Fix #5452

tests/core/sys/windows/util.odin

@@ -0,0 +1,33 @@
+#+build windows
+package test_core_sys_windows
+
+import "base:intrinsics"
+import "core:testing"
+import win32 "core:sys/windows"
+
+UTF16_Vector :: struct {
+	wstr: win32.wstring,
+	ustr: string,
+}
+
+utf16_vectors := []UTF16_Vector{
+	{
+		intrinsics.constant_utf16_cstring("Hellope, World!"),
+		"Hellope, World!",
+	},
+	{
+		intrinsics.constant_utf16_cstring("Hellope\x00, World!"),
+		"Hellope",
+	},
+}
+
+@(test)
+utf16_to_utf8_buf_test :: proc(t: ^testing.T) {
+	for test in utf16_vectors {
+		buf := make([]u8, len(test.ustr))
+		defer delete(buf)
+
+		res := win32.utf16_to_utf8_buf(buf[:], test.wstr[:len(test.ustr)])
+		testing.expect_value(t, res, test.ustr)
+	}
+}