Add jest config

__mocks__/file-mock.js

@@ -0,0 +1 @@
+module.exports = "test-file-stub"

__mocks__/gatsby.js

@@ -0,0 +1,27 @@
+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

@@ -0,0 +1,8 @@
+// Configuration file for Jest testing
+// https://www.gatsbyjs.com/docs/unit-testing/
+
+const babelOptions = {
+  presets: ["babel-preset-gatsby"],
+}
+
+module.exports = require("babel-jest").createTransformer(babelOptions)

jest.config.js

@@ -0,0 +1,16 @@
+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`, `<rootDir>.*/public`],
+  transformIgnorePatterns: [`node_modules/(?!(gatsby)/)`],
+  globals: {
+    __PATH_PREFIX__: ``,
+  },
+  testURL: `http://localhost`,
+  setupFiles: [`<rootDir>/loadershim.js`],
+}

loadershim.js

@@ -0,0 +1,3 @@
+global.___loader = {
+  enqueue: jest.fn(),
+}

package.json

@@ -55,10 +55,15 @@
     "styled-system": "^5.1.5"
   },
   "devDependencies": {
+    "babel-jest": "^26.6.3",
+    "babel-preset-gatsby": "^0.8.0",
     "github-slugger": "^1.3.0",
     "husky": "^4.2.5",
     "prettier": "^2.2.1",
-    "pretty-quick": "^3.1.0"
+    "pretty-quick": "^3.1.0",
+    "identity-obj-proxy": "^3.0.0",
+    "jest": "^26.6.3",
+    "react-test-renderer": "^17.0.1"
   },
   "scripts": {
     "build": "yarn copy-contributors && yarn build:app && yarn build:lambda",
@@ -71,7 +76,7 @@
     "start": "gatsby develop",
     "start:static": "gatsby build && gatsby serve",
     "serve": "gatsby serve",
-    "test": "echo \"Write tests! -> https://gatsby.dev/unit-testing\" && exit 1"
+    "test": "jest"
   },
   "husky": {
     "hooks": {