diff --git a/data_structures/arrays/monotonic_array.py b/data_structures/arrays/monotonic_array.py
index c50a21530814..729c63b0df46 100644
--- a/data_structures/arrays/monotonic_array.py
+++ b/data_structures/arrays/monotonic_array.py
@@ -1,3 +1,6 @@
+import doctest
+
+
 # https://leetcode.com/problems/monotonic-array/
 def is_monotonic(nums: list[int]) -> bool:
     """
@@ -9,6 +12,16 @@ def is_monotonic(nums: list[int]) -> bool:
     True
     >>> is_monotonic([1, 3, 2])
     False
+    >>> is_monotonic([1,2,3,4,5,6,5])
+    False
+    >>> is_monotonic([-3,-2,-1])
+    True
+    >>> is_monotonic([-5,-6,-7])
+    True
+    >>> is_monotonic([0,0,0])
+    True
+    >>> is_monotonic([-100,0,100])
+    True
     """
     return all(nums[i] <= nums[i + 1] for i in range(len(nums) - 1)) or all(
         nums[i] >= nums[i + 1] for i in range(len(nums) - 1)
@@ -21,3 +34,5 @@ def is_monotonic(nums: list[int]) -> bool:
     print(is_monotonic([1, 2, 2, 3]))  # Output: True
     print(is_monotonic([6, 5, 4, 4]))  # Output: True
     print(is_monotonic([1, 3, 2]))  # Output: False
+
+    doctest.testmod()