Add faulty circle_area function and tests

drone_test/__init__.py

@@ -0,0 +1,12 @@
+"""Python module to test drone builds"""
+
+import math
+
+def circle_area(radius: float):
+    """Calculate the area of a circle
+
+    :param radius: circle radius
+    :raises ValueError: radius is negative
+    :return: area of the circle
+    """
+    return math.pi * radius ** 2