diff --git a/src/one.rs b/src/one.rs
index 8eaa076..1498a50 100644
--- a/src/one.rs
+++ b/src/one.rs
@@ -7,11 +7,21 @@ pub struct Args {
 }
 
 impl Problem for Args {
-    // We could derive it mathematically, ... or write a dump loop
-    fn solve(self, _: GlobalArgs) -> color_eyre::Result<()> {
-        let sum: u64 = (0..self.until).filter(|x| x % 3 == 0 || x % 5 == 0).sum();
-        println!("Sum of 0..{}: {}", self.until, sum);
+    type Solution = u64;
 
-        Ok(())
+    // We could derive it mathematically, ... or write a dump loop
+    fn solve(self, _: GlobalArgs) -> color_eyre::Result<u64> {
+        let sum = (0..self.until).filter(|x| x % 3 == 0 || x % 5 == 0).sum();
+
+        Ok(sum)
     }
 }
+
+#[cfg(test)]
+#[test]
+fn rsp() {
+    assert_eq!(
+        Args { until: 1000 }.solve(GlobalArgs::default()).unwrap(),
+        233168
+    );
+}