Added doctests for fibonacci.py (TheAlgorithms#10836)

* added other possible cases

* added test for correct output of truth table

* few fibonacci tests added

* updating DIRECTORY.md

* Update nor_gate.py

* updating DIRECTORY.md

* Update fibonacci.py

removed whitespace

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Diff for: maths/fibonacci.py

@@ -81,6 +81,18 @@ def fib_recursive(n: int) -> list[int]:
     def fib_recursive_term(i: int) -> int:
         """
         Calculates the i-th (0-indexed) Fibonacci number using recursion
+        >>> fib_recursive_term(0)
+        0
+        >>> fib_recursive_term(1)
+        1
+        >>> fib_recursive_term(5)
+        5
+        >>> fib_recursive_term(10)
+        55
+        >>> fib_recursive_term(-1)
+        Traceback (most recent call last):
+            ...
+        Exception: n is negative
         """
         if i < 0:
             raise Exception("n is negative")
@@ -197,6 +209,10 @@ def fib_binet(n: int) -> list[int]:
 
 
 if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+
     num = 30
     time_func(fib_iterative, num)
     time_func(fib_recursive, num)  # Around 3s runtime