Added tests for main component

src/__tests__/index.test.js

+import Vue from 'vue';
+import json from '../../fixtures/file.json';
+import Notebook from '../index';
+
+const Component = Vue.extend(Notebook);
+
+describe('Notebook component', () => {
+  let vm;
+
+  describe('without JSON', () => {
+    beforeEach((done) => {
+      vm = new Component({
+        propsData: {
+          notebook: {},
+        },
+      });
+      vm.$mount();
+
+      setTimeout(() => {
+        done();
+      });
+    });
+
+    test('does not render', () => {
+      expect(vm.$el.tagName).toBeUndefined();
+    });
+  });
+
+  describe('with JSON', () => {
+    beforeEach((done) => {
+      vm = new Component({
+        propsData: {
+          notebook: json,
+        },
+      });
+      vm.$mount();
+
+      setTimeout(() => {
+        done();
+      });
+    });
+
+    test('renders cells', () => {
+      expect(vm.$el.querySelectorAll('.cell').length).toBe(2);
+    });
+
+    test('renders markdown cell', () => {
+      expect(vm.$el.querySelector('.markdown')).not.toBeNull();
+    });
+
+    test('renders code cell', () => {
+      expect(vm.$el.querySelector('pre')).not.toBeNull();
+    });
+  });
+});