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

jest.config.js

@@ -0,0 +1,17 @@
+module.exports = {
+  transform: {
+    '^.+\\.jsx?$': `<rootDir>/jest-preprocess.js`,
+  },
+  moduleNameMapper: {
+    '.+\\.(css|styl|less|sass|scss)$': `identity-obj-proxy`,
+    '.+\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$': `<rootDir>/__mocks__/file-mock.js`,
+  },
+  testPathIgnorePatterns: [`node_modules`, `\\.cache`],
+  transformIgnorePatterns: [`node_modules/(?!(gatsby)/)`],
+  globals: {
+    __PATH_PREFIX__: ``,
+  },
+  testURL: `http://localhost`,
+  setupFilesAfterEnv: [`<rootDir>/jest.setup.js`],
+  setupFiles: [`<rootDir>/loadershim.js`],
+};