diff --git a/test/compile_cache_test.rb b/test/compile_cache_test.rb
index 5a8636f4..e10d0f38 100644
--- a/test/compile_cache_test.rb
+++ b/test/compile_cache_test.rb
@@ -37,7 +37,7 @@ def test_no_write_permission_to_cache
       # read-only files.
       pass
     else
-      path = Help.set_file("a.rb", "a = 3", 100)
+      path = Help.set_file("a.rb", "a = a = 3", 100)
       folder = File.dirname(Help.cache_path(@tmp_dir, path))
       FileUtils.mkdir_p(folder)
       FileUtils.chmod(0o400, folder)