diff --git a/src/lib.rs b/src/lib.rs
index 8012e57..0f0e76f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -920,4 +920,103 @@ mod tests {
 
         assert_eq!(col1, col2);
     }
+
+    #[test]
+    fn test_get_diagonal_valid() {
+        let m = Matrix {
+            rows: 3,
+            columns: 3,
+            data: vec![
+                Fraction::from(1),
+                Fraction::from(2),
+                Fraction::from(3),
+                Fraction::from(4),
+                Fraction::from(5),
+                Fraction::from(6),
+                Fraction::from(7),
+                Fraction::from(8),
+                Fraction::from(9),
+            ],
+        };
+
+        let diag: Vec<Fraction> = m.get_diagonal().unwrap().cloned().collect();
+
+        assert_eq!(
+            diag,
+            vec![Fraction::from(1), Fraction::from(5), Fraction::from(9)]
+        );
+    }
+
+    #[test]
+    fn test_get_diagonal_single_element() {
+        let m = Matrix::new(1, 1, Fraction::from(42)).unwrap();
+
+        let diag: Vec<Fraction> = m.get_diagonal().unwrap().cloned().collect();
+
+        assert_eq!(diag, vec![Fraction::from(42)]);
+    }
+
+    #[test]
+    fn test_get_diagonal_identity_like() {
+        let mut data = vec![Fraction::from(0); 9];
+        data[0] = Fraction::from(1);
+        data[4] = Fraction::from(1);
+        data[8] = Fraction::from(1);
+
+        let m = Matrix {
+            rows: 3,
+            columns: 3,
+            data,
+        };
+
+        let diag: Vec<Fraction> = m.get_diagonal().unwrap().cloned().collect();
+
+        assert_eq!(
+            diag,
+            vec![Fraction::from(1), Fraction::from(1), Fraction::from(1)]
+        );
+    }
+
+    #[test]
+    fn test_get_diagonal_not_squared() {
+        let m = Matrix::new(2, 3, Fraction::from(0)).unwrap();
+
+        let result = m.get_diagonal();
+
+        assert!(matches!(result, Err(MatrixError::NotSquared)));
+    }
+
+    #[test]
+    fn test_get_diagonal_matches_get() {
+        let m = Matrix {
+            rows: 4,
+            columns: 4,
+            data: (0..16).map(|x| Fraction::from(x)).collect(),
+        };
+
+        let diag = m.get_diagonal().unwrap();
+
+        for (i, val) in diag.enumerate() {
+            assert_eq!(*val, *m.get(i, i).unwrap());
+        }
+    }
+
+    #[test]
+    fn test_get_diagonal_length() {
+        let m = Matrix::new(5, 5, Fraction::from(3)).unwrap();
+
+        let diag: Vec<Fraction> = m.get_diagonal().unwrap().cloned().collect();
+
+        assert_eq!(diag.len(), 5);
+    }
+
+    #[test]
+    fn test_get_diagonal_iterator_repeatability() {
+        let m = Matrix::new(3, 3, Fraction::from(7)).unwrap();
+
+        let d1: Vec<Fraction> = m.get_diagonal().unwrap().cloned().collect();
+        let d2: Vec<Fraction> = m.get_diagonal().unwrap().cloned().collect();
+
+        assert_eq!(d1, d2);
+    }
 }