all symmetricDif tests passing

src/setSymmetricDifference.js

@@ -0,0 +1,14 @@
+export default function setSymmetricDifference(firstSet, secondSet) {
+
+  const intersection = new Set([...firstSet].filter(x => !secondSet.includes(x)))
+  const intersection2 = new Set([...secondSet].filter(x => !firstSet.includes(x)))
+
+  const intersectionArray = Array.from(intersection)
+  const intersectionArray2 = Array.from(intersection2)
+
+  const setArray = intersectionArray.concat(intersectionArray2)
+
+  if (!firstSet || !secondSet) {
+    return undefined
+  } return setArray
+}

test/setSymmetricDifference_test.js

@@ -0,0 +1,24 @@
+import { expect } from 'chai';
+import setSymmetricDifference from '../src/setSymmetricDifference';
+
+describe('setSymmetricDifference()', () => {
+  it('should be a function', () => {
+    expect(setSymmetricDifference).to.be.a('function');
+  });
+
+  it('Return the symmetric difference of two sets.', () => {
+    const firstSet = [1, 2, 3, 4];
+    const secondSet = [2, 4, 6, 8];
+    expect(setSymmetricDifference(firstSet, secondSet)).to.deep.equal([1, 3, 6, 8]);
+  });
+
+  it('Return the symmetric difference of two sets.', () => {
+    const firstSet = [3, 6, 9, 12];
+    const secondSet = [6, 7, 8, 9];
+    expect(setSymmetricDifference(firstSet, secondSet)).to.deep.equal([3, 12, 7, 8]);
+  });
+
+  it('Will not try to evaluate empty things', () => {
+    expect(setSymmetricDifference('', '')).to.equal(undefined);
+  });
+});