Set up Unit Testing environment with Gatsby, Jest and @testing-library/react; added some basic unit tests for Castform template

src/templates/__tests__/Castform.test.js

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+import React from 'react';
+import { render, cleanup } from '@testing-library/react';
+import path from 'path';
+import fs from 'fs';
+
+import '../../i18n/index';
+import Castform from '../Castform';
+
+let data = {};
+
+beforeEach(() => {
+  const filePath = path.resolve(__dirname, '../../data/initialState.json');
+  const file = fs.readFileSync(filePath);
+  data = JSON.parse(file);
+});
+
+afterEach(cleanup);
+
+it('renders correctly', () => {
+  const { container } = render(<Castform data={data} />);
+
+  expect(container).toBeTruthy();
+  expect(container).toBeInTheDocument();
+});
+
+describe('date of birth', () => {
+  const birthDateLabelMatcher = /Date of birth/i;
+
+  it('is not shown if not provided', () => {
+    const { queryByText } = render(<Castform data={data} />);
+
+    expect(queryByText(birthDateLabelMatcher)).toBe(null);
+  });
+
+  it('is shown if provided', () => {
+    const birthDate = new Date(1990, 0, 20);
+    const birthDateFormatted = '20 January 1990';
+    data.profile.birthDate = birthDate;
+
+    const { getByText } = render(<Castform data={data} />);
+
+    expect(getByText(birthDateLabelMatcher)).toBeTruthy();
+    expect(getByText(birthDateLabelMatcher)).toBeInTheDocument();
+    expect(getByText(birthDateFormatted)).toBeTruthy();
+    expect(getByText(birthDateFormatted)).toBeInTheDocument();
+  });
+});