Updated the test system

test/distance.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {distance} = require('./_30s.js');
+
+test('distance is a Function', () => {
+  expect(distance).toBeInstanceOf(Function);
+});
+test('Calculates the distance between two points', () => {
+  expect(distance(1, 1, 2, 3)).toBeCloseTo(2.23606797749979, 5);
+});