Updated the test system

test/symmetricDifferenceWith.test.js

@@ -0,0 +1,15 @@
+const expect = require('expect');
+const {symmetricDifferenceWith} = require('./_30s.js');
+
+test('symmetricDifferenceWith is a Function', () => {
+  expect(symmetricDifferenceWith).toBeInstanceOf(Function);
+});
+test('Returns the symmetric difference between two arrays, using a provided function as a comparator', () => {
+  expect(
+    symmetricDifferenceWith(
+      [1, 1.2, 1.5, 3, 0],
+      [1.9, 3, 0, 3.9],
+      (a, b) => Math.round(a) === Math.round(b)
+    )
+  ).toEqual([1, 1.2, 3.9]);
+});