chore: update mocks, move configs to jest dir

jest/__mocks__/fileMock.js

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+'use strict';
+
+module.exports = 'file';

jest/__mocks__/gatsby.js

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+'use strict';
+
+const React = require('react');
+
+const gatsby = jest.requireActual('gatsby');
+
+module.exports = {
+  ...gatsby,
+  graphql: jest.fn(),
+  Link: jest.fn().mockImplementation(
+    ({
+      activeClassName,
+      activeStyle,
+      getProps,
+      innerRef,
+      ref,
+      replace,
+      to,
+      ...rest
+    }) => (
+      React.createElement('a', {
+        ...rest,
+        href: to,
+      })
+    )
+  ),
+  StaticQuery: jest.fn(),
+  useStaticQuery: jest.fn(),
+};

jest/jest-config.js

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+'use strict';
+
+module.exports = {
+  rootDir: '../',
+  transform: {
+    '^.+\\.js?$': '<rootDir>/tests/jest-preprocess.js'
+  },
+  testMatch: ['**/__tests__/**/*.js', '**/?(*.)test.js'],
+  moduleNameMapper: {
+    '.+\\.(css|styl|less|sass|scss)$': 'identity-obj-proxy',
+    '.+\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$': '<rootDir>/tests/__mocks__/fileMock.js'
+  },
+  testPathIgnorePatterns: ['node_modules', '.cache', 'public'],
+  transformIgnorePatterns: [
+    'node_modules/(?!(gatsby)/)'
+  ],
+  globals: {
+    __PATH_PREFIX__: ''
+  },
+  testURL: 'http://localhost/',
+  setupFiles: ['<rootDir>/tests/loadershim.js']
+};

jest/jest-preprocess.js

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+'use strict';
+
+const babelOptions = {
+  presets: [
+    '@babel/react',
+    '@babel/env',
+    'babel-preset-gatsby'
+  ],
+  plugins: [
+    '@babel/plugin-proposal-optional-chaining',
+    '@babel/plugin-proposal-class-properties',
+    '@babel/plugin-transform-flow-strip-types',
+  ],
+};
+
+module.exports = require('babel-jest').createTransformer(babelOptions);

jest/loadershim.js

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+'use strict';
+
+global.___loader = {
+  enqueue: jest.fn(),
+};