factor::factor: Add integration tests

src/uu/factor/src/factor.rs

@@ -47,6 +47,13 @@ impl Factors {
     fn push(&mut self, prime: u64) {
         self.add(prime, 1)
     }
+
+    #[cfg(test)]
+    fn product(&self) -> u64 {
+        self.f
+            .iter()
+            .fold(1, |acc, (p, exp)| acc * p.pow(*exp as u32))
+    }
 }
 
 impl ops::MulAssign<Factors> for Factors {
@@ -132,3 +139,22 @@ pub fn uumain(args: Vec<String>) -> i32 {
     }
     0
 }
+
+#[cfg(test)]
+mod tests {
+    use super::factor;
+
+    #[test]
+    fn factor_recombines_small() {
+        assert!((1..10_000)
+            .map(|i| 2 * i + 1)
+            .all(|i| factor(i).product() == i));
+    }
+
+    #[test]
+    fn factor_recombines_overflowing() {
+        assert!((0..250)
+            .map(|i| 2 * i + 2u64.pow(32) + 1)
+            .all(|i| factor(i).product() == i));
+    }
+}