Migrate to jest (#1520)

Mocha doesn't have a lot of features provided by jest.
There is a great assertion library out of the box.
And the most cool feature is inline snapshots.
Mocha also hides errors which makes debugging a nightmare sometimes.

test/jsapi/_index.test.js

@@ -0,0 +1,24 @@
+'use strict';
+
+const { createContentItem } = require('../../lib/svgo.js');
+const JSAPI = require('../../lib/svgo/jsAPI.js');
+
+describe('svgo api', function () {
+  it('should has createContentItem method', function () {
+    expect(createContentItem).toBeInstanceOf(Function);
+  });
+
+  it('should be able to create content item', function () {
+    var item = createContentItem({
+      elem: 'elementName',
+    });
+    expect(item).toBeInstanceOf(JSAPI);
+    expect(item.elem).toEqual('elementName');
+  });
+
+  it('should be able create content item without argument', function () {
+    var item = createContentItem();
+    expect(item).toBeInstanceOf(JSAPI);
+    expect(item).toEqual({});
+  });
+});