Add example of finding a bug using fuzz testing

Author: gjbex

source-code/testing/Hypothesis/README.md

@@ -10,6 +10,7 @@ uses fuzzing to find issues in your code.
    function.
 1. `test_factorial.py`: hypothesis tests of the factorial
    function
+1. `points.py`: example of finding a bug with fuzz testing.
 
 
 ## How to use it?

source-code/testing/Hypothesis/points.py

@@ -0,0 +1,54 @@
+import math
+from hypothesis import given, strategies as st
+
+
+class Point:
+
+    _x: float
+    _y: float
+
+    def __init__(self, x: float, y: float):
+        self._x = float(x)
+        self._y = float(y)
+
+    @property
+    def x(self):
+        return self._x
+
+    @x.setter
+    def x(self, x):
+        self._x = float(x)
+
+    @property
+    def y(self):
+        return self._y
+
+    @y.setter
+    def y(self, y):
+        self._y = float(y)
+
+    def __repr__(self):
+        return f'Point({self._x}, {self._y})'
+
+    def __str__(self):
+        return f'({self._x}, {self._y})'
+
+    def distance(self, other):
+        return math.sqrt((self._x - other._x)**2 + (self._y - other._y)**2)
+
+    def is_on_line(self, p1, p2):
+        return math.isclose(self.y - ((p2.y - p1.y)*self.x - p1.x*p2.y + p2.x*p1.y)/(p2.x - p1.x), 0.0)
+
+
+def test_distance():
+    p1 = Point(0, 0)
+    p2 = Point(3, 4)
+    assert math.isclose(p1.distance(p2), 5.0)
+
+
+@given(x1=st.floats(), y1=st.floats(), x2=st.floats(), y2=st.floats(), x=st.floats(), y=st.floats())
+def test_is_on_line(x1: float, y1: float, x2: float, y2: float, x: float, y: float):
+    p1 = Point(x1, y1)
+    p2 = Point(x2, y2)
+    p = Point(x, y)
+    assert p.is_on_line(p1, p2)