diff --git a/src/lib.rs b/src/lib.rs
index 0f0e76f..ad072d2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1019,4 +1019,90 @@ mod tests {
 
         assert_eq!(d1, d2);
     }
+
+    #[test]
+    fn test_set_valid_position() {
+        let mut m = Matrix::new(2, 2, Fraction::from(0)).unwrap();
+
+        m.set(0, 1, Fraction::from(5)).unwrap();
+
+        assert_eq!(*m.get(0, 1).unwrap(), Fraction::from(5));
+    }
+
+    #[test]
+    fn test_set_first_element() {
+        let mut m = Matrix::new(3, 3, Fraction::from(0)).unwrap();
+
+        m.set(0, 0, Fraction::from(9)).unwrap();
+
+        assert_eq!(*m.get(0, 0).unwrap(), Fraction::from(9));
+    }
+
+    #[test]
+    fn test_set_last_element() {
+        let mut m = Matrix::new(2, 2, Fraction::from(0)).unwrap();
+
+        m.set(1, 1, Fraction::from(7)).unwrap();
+
+        assert_eq!(*m.get(1, 1).unwrap(), Fraction::from(7));
+    }
+
+    #[test]
+    fn test_set_out_of_bounds_row() {
+        let mut m = Matrix::new(2, 2, Fraction::from(0)).unwrap();
+
+        let result = m.set(2, 0, Fraction::from(1));
+
+        assert!(matches!(result, Err(MatrixError::IndexOutOfRange)));
+    }
+
+    #[test]
+    fn test_set_out_of_bounds_column() {
+        let mut m = Matrix::new(2, 2, Fraction::from(0)).unwrap();
+
+        let result = m.set(0, 2, Fraction::from(1));
+
+        assert!(matches!(result, Err(MatrixError::IndexOutOfRange)));
+    }
+
+    #[test]
+    fn test_set_does_not_affect_other_elements() {
+        let mut m = Matrix::new(2, 2, Fraction::from(1)).unwrap();
+
+        m.set(0, 1, Fraction::from(99)).unwrap();
+
+        // solo cambia ese elemento
+        assert_eq!(*m.get(0, 0).unwrap(), Fraction::from(1));
+        assert_eq!(*m.get(0, 1).unwrap(), Fraction::from(99));
+        assert_eq!(*m.get(1, 0).unwrap(), Fraction::from(1));
+        assert_eq!(*m.get(1, 1).unwrap(), Fraction::from(1));
+    }
+
+    #[test]
+    fn test_set_overwrite_value() {
+        let mut m = Matrix::new(2, 2, Fraction::from(3)).unwrap();
+
+        m.set(1, 0, Fraction::from(8)).unwrap();
+        m.set(1, 0, Fraction::from(10)).unwrap();
+
+        assert_eq!(*m.get(1, 0).unwrap(), Fraction::from(10));
+    }
+
+    #[test]
+    fn test_set_consistency_with_manual_index() {
+        let mut m = Matrix {
+            rows: 3,
+            columns: 3,
+            data: vec![Fraction::from(0); 9],
+        };
+
+        for r in 0..3 {
+            for c in 0..3 {
+                let val = Fraction::from((r * 3 + c) as i64);
+                m.set(r, c, val.clone()).unwrap();
+
+                assert_eq!(*m.get(r, c).unwrap(), val);
+            }
+        }
+    }
 }