diff --git a/app-proto/src/assembly.rs b/app-proto/src/assembly.rs
index fe08c91..dc0bf91 100644
--- a/app-proto/src/assembly.rs
+++ b/app-proto/src/assembly.rs
@@ -535,8 +535,8 @@ mod tests {
             let subjects = [0, 1].map(|k| {
                 elts.insert(
                     Element::new(
-                        "sphere{k}".to_string(),
-                        "Sphere {k}".to_string(),
+                        format!("sphere{k}"),
+                        format!("Sphere {k}"),
                         [1.0_f32, 1.0_f32, 1.0_f32],
                         engine::sphere(0.0, 0.0, 0.0, 1.0)
                     )