test: adding more tests to missing number algorithm
diff --git a/bit_manipulation/missing_number.py b/bit_manipulation/missing_number.py
index 32b949daa717..554887b17562 100644
--- a/bit_manipulation/missing_number.py
+++ b/bit_manipulation/missing_number.py
@@ -11,6 +11,12 @@ def find_missing_number(nums: list[int]) -> int:
     Example:
         >>> find_missing_number([0, 1, 3, 4])
         2
+        >>> find_missing_number([4, 3, 1, 0])
+        2
+        >>> find_missing_number([-4, -3, -1, 0])
+        -2
+        >>> find_missing_number([-2, 2, 1, 3, 0])
+        -1
         >>> find_missing_number([1, 3, 4, 5, 6])
         2
         >>> find_missing_number([6, 5, 4, 2, 1])
@@ -26,3 +32,9 @@ def find_missing_number(nums: list[int]) -> int:
         missing_number ^= i ^ nums[i - low]
 
     return missing_number
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()

### Describe your change:
Adding more tests to missing number algorithm
Fixes #9943 

* [ ] Add an algorithm?
* [ ] Fix a bug or typo in an existing algorithm?
* [ ] Documentation change?
* [X] Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.

### Checklist:
* [x] I have read [CONTRIBUTING.md](https://github.com/TheAlgorithms/Python/blob/master/CONTRIBUTING.md).
* [x] This pull request is all my own work -- I have not plagiarized.
* [x] I know that pull requests will not be merged if they fail the automated tests.
* [x] This PR only changes one algorithm file.  To ease review, please open separate PRs for separate algorithms.
* [x] All new Python files are placed inside an existing directory.
* [x] All filenames are in all lowercase characters with no spaces or dashes.
* [x] All functions and variable names follow Python naming conventions.
* [x] All function parameters and return values are annotated with Python [type hints](https://docs.python.org/3/library/typing.html).
* [x] All functions have [doctests](https://docs.python.org/3/library/doctest.html) that pass the automated testing.
* [x] All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
* [x] If this pull request resolves one or more open issues then the description above includes the issue number(s) with a [closing keyword](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue): "Fixes #ISSUE-NUMBER".
