🛠 set up jest for gatsby + typescript

__mocks__/file-mock.js

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+// See: https://www.gatsbyjs.org/docs/unit-testing/#2-creating-a-configuration-file-for-jest
+
+module.exports = 'test-file-stub'

__mocks__/gatsby.js

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+// See: https://www.gatsbyjs.org/docs/unit-testing/#3-useful-mocks-to-complete-your-testing-environment
+
+const React = require('react')
+const gatsby = jest.requireActual('gatsby')
+
+module.exports = {
+  ...gatsby,
+  graphql: jest.fn(),
+  Link: jest.fn().mockImplementation(
+    // these props are invalid for an `a` tag
+    ({
+      activeClassName,
+      activeStyle,
+      getProps,
+      innerRef,
+      partiallyActive,
+      ref,
+      replace,
+      to,
+      ...rest
+    }) =>
+      React.createElement('a', {
+        ...rest,
+        href: to,
+      })
+  ),
+  StaticQuery: jest.fn(),
+  useStaticQuery: jest.fn(),
+}

jest-preprocess.js

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+// See: https://www.gatsbyjs.org/docs/unit-testing/#2-creating-a-configuration-file-for-jest
+
+const babelOptions = {
+  presets: ['babel-preset-gatsby'],
+}
+
+module.exports = require('babel-jest').createTransformer(babelOptions)

jest.config.js

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+// See: https://www.gatsbyjs.org/docs/unit-testing/
+
+module.exports = {
+  transform: {
+    '^.+\\.tsx?$': 'ts-jest',
+    '^.+\\.jsx?$': '<rootDir>/jest-preprocess.js',
+  },
+  testRegex: '(/__tests__/.*|(\\.|/)(test|spec))\\.([tj]sx?)$',
+  moduleNameMapper: {
+    '.+\\.(css|styl|less|sass|scss)$': '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',
+  },
+  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node'],
+  testEnvironment: 'jest-environment-jsdom',
+  testPathIgnorePatterns: ['node_modules', '.cache', 'public'],
+  transformIgnorePatterns: ['node_modules/(?!(gatsby)/)'],
+  globals: {
+    __PATH_PREFIX__: '',
+  },
+  setupFiles: ['<rootDir>/loadershim.js'],
+}

loadershim.js

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+global.___loader = {
+  enqueue: jest.fn(),
+}