diff --git a/src/io.rs b/src/io.rs
index d356bb5..d2931b9 100644
--- a/src/io.rs
+++ b/src/io.rs
@@ -444,7 +444,7 @@ mod tests {
         assert!(ts[0].len() == 5000);
         println!("{:?}", ts);
         for (actual, expected) in ts[1].iter().zip(expected.iter()) {
-            assert!((actual-expected).abs() < 0.001, format!("{:?} != {:?}", actual, expected));
+            assert!((actual-expected).abs() < 0.001, "{:?} != {:?}", actual, expected);
         }
     }
 
@@ -601,4 +601,4 @@ mod tests {
         assert_approx_eq!(test[2].0, 5.0);
         assert_approx_eq!(test[2].1, 30.0);
     }
-}
\ No newline at end of file
+}