Added unit test for example component

examples/svelte-kitchen-sink/src/components/Button.test.js

@@ -0,0 +1,23 @@
+import { document } from 'global';
+import Button from './Button.svelte';
+
+let target;
+let component;
+
+describe('Button Component', () => {
+  beforeEach(() => {
+    target = document.createElement('div');
+
+    component = new Button({ target });
+  });
+
+  it('should render `text` property', () => {
+    const text = 'Hello world';
+
+    component.set({ text });
+
+    const componentText = target.firstChild.textContent.trim();
+
+    expect(componentText).toEqual(text);
+  });
+});