Merge pull request 'Add cross-product and tests' (#9) from enh/cross-product into unit_tests

Reviewed-on: #9

src/fancymath/vector.py

@@ -36,6 +36,14 @@ class Vector(object):
         z = self.z + other.z
         return self.__class__(x, y, z)
 
+    def __mul__(self, other):
+        if not isinstance(other, Vector):
+            return NotImplemented
+        x = self.y * other.z - self.z * other.y
+        y = self.z * other.x - self.x * other.z
+        z = self.x * other.y - self.y * other.x
+        return self.__class__(x, y, z)
+
 
 if __name__ == "__main__":
     v1 = Vector(3, 4, 0)

test/test_vector.py

@@ -4,6 +4,28 @@ from fancymath.vector import Vector
 
 
 class TestVector(unittest.TestCase):
+    def test_cross_product(self):
+        # given
+        v1 = Vector(1, 2, 3)
+        v2 = Vector(3, 2, 1)
+
+        # when
+        v3 = v1 * v2
+
+        # then
+        self.assertIsInstance(v3, Vector)
+        self.assertEqual(v3.x, -4)
+        self.assertEqual(v3.y, 8)
+        self.assertEqual(v3.z, -4)
+
+    def test_cross_product_failure(self):
+        v1 = Vector(1, 2, 3)
+        v2 = (3, 2, 1)
+
+        with self.assertRaises(TypeError):
+            v1 * v2
+
+
     def test_add_vector(self):
         v1 = Vector(1, 2, 3)
         v2 = Vector(-3, -2, -1)