diff --git a/DIRECTORY.md b/DIRECTORY.md
index 1e3711fe8dda..61823a241c8d 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -826,6 +826,7 @@
   * [Shear Stress](physics/shear_stress.py)
   * [Speed Of Sound](physics/speed_of_sound.py)
   * [Speeds Of Gas Molecules](physics/speeds_of_gas_molecules.py)
+  * [Terminal Velocity](physics/terminal_velocity.py)
 
 ## Project Euler
   * Problem 001
diff --git a/maths/fibonacci.py b/maths/fibonacci.py
index e810add69dc7..8cdd6cdb160e 100644
--- a/maths/fibonacci.py
+++ b/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