diff --git a/src/lib.rs b/src/lib.rs
index ed79fe1..2b11f08 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -104,7 +104,7 @@ impl ops::Add for Fraction {
     fn add(self, other: Self) -> Self::Output {
         let mut new = Fraction {
             num: (self.num * other.den) + (self.den * other.num),
-            den: self.num * other.den,
+            den: self.den * other.den,
         };
         new.reduce();
         new.correct_sign();
@@ -248,4 +248,49 @@ mod tests {
         assert_eq!(f.num, -1);
         assert_eq!(f.den, 2);
     }
+
+    #[test]
+    fn test_add_basic() {
+        let a = Fraction::new(7, 13).unwrap();
+        let b = Fraction::new(4, 7).unwrap();
+        let c = a + b;
+        assert_eq!(c.num, 101);
+        assert_eq!(c.den, 91);
+    }
+
+    #[test]
+    fn test_add_with_common_denominator() {
+        let a = Fraction::new(7, 13).unwrap();
+        let b = Fraction::new(4, 13).unwrap();
+        let c = a + b;
+        assert_eq!(c.num, 11);
+        assert_eq!(c.den, 13);
+    }
+
+    #[test]
+    fn test_add_positive_and_negative() {
+        let a = Fraction::new(-32, 237).unwrap();
+        let b = Fraction::new(22, 44).unwrap();
+        let c = a + b;
+        assert_eq!(c.num, 173);
+        assert_eq!(c.den, 474);
+    }
+
+    #[test]
+    fn test_add_negative_and_negative() {
+        let a = Fraction::new(-500, 12).unwrap();
+        let b = Fraction::new(-22, 4).unwrap();
+        let c = a + b;
+        assert_eq!(c.num, -283);
+        assert_eq!(c.den, 6);
+    }
+
+    #[test]
+    fn test_add_with_zero() {
+        let a = Fraction::new(0, 13).unwrap();
+        let b = Fraction::new(4, 7).unwrap();
+        let c = a + b;
+        assert_eq!(c.num, 4);
+        assert_eq!(c.den, 7);
+    }
 }