Add visual css testing tools

.gitignore

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 /css
 /dist
+/node_modules

__tests__/zumer-examples.spec.js

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+const puppeteer = require('puppeteer');
+
+describe('Test Zumer CSS examples', () => {
+  let browser;
+
+  beforeAll(async () => {
+    browser = await puppeteer.launch({
+      headless: 'new',
+      // `headless: true` (default) enables old Headless;
+      // `headless: 'new'` enables new Headless;
+      // `headless: false` enables “headful” mode.
+    });
+  });
+
+  it('Index', async () => {
+    const page = await browser.newPage();
+    await page.goto('http://localhost:5500/examples/');
+    const image = await page.screenshot();
+
+    expect(image).toMatchImageSnapshot();
+  });
+
+  it('Generic', async () => {
+    const page = await browser.newPage();
+    await page.goto('http://localhost:5500/examples/generic.html');
+    const image = await page.screenshot();
+
+    expect(image).toMatchImageSnapshot();
+  });
+
+  it('Spread', async () => {
+    const page = await browser.newPage();
+    await page.goto('http://localhost:5500/examples/spread.html');
+    const image = await page.screenshot();
+
+    expect(image).toMatchImageSnapshot();
+  });
+
+  it('Watch', async () => {
+    const page = await browser.newPage();
+    await page.goto('http://localhost:5500/examples/watch.html');
+    const image = await page.screenshot();
+
+    expect(image).toMatchImageSnapshot();
+  });
+
+  it('Sector grid', async () => {
+    const page = await browser.newPage();
+    await page.goto('http://localhost:5500/examples/arcgrid.html');
+    const image = await page.screenshot();
+
+    expect(image).toMatchImageSnapshot();
+  });
+
+  afterAll(async () => {
+    await browser.close();
+  });
+});

jest-setup.js

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+/*
+ * Copyright (c) 2018 American Express Travel Related Services Company, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+// eslint runs from root and only looks at root package.json
+// eslint-disable-next-line import/no-unresolved
+const { toMatchImageSnapshot } = require('jest-image-snapshot');
+
+expect.extend({ toMatchImageSnapshot });