extend jsdom testing environment with TextEncoder/TextDecoder

Author: lobsterkatie

.jest/dom-environment.js

@@ -0,0 +1,17 @@
+const JSDOMEnvironment = require('jest-environment-jsdom');
+
+// TODO Node >= 8.3 includes the same TextEncoder and TextDecoder as exists in the browser, but they haven't yet been
+// added to jsdom. Until they are, we can do it ourselves. Once they do, this file can go away.
+
+// see https://github.com/jsdom/jsdom/issues/2524 and https://nodejs.org/api/util.html#util_class_util_textencoder
+
+module.exports = class DOMEnvironment extends JSDOMEnvironment {
+  async setup() {
+    await super.setup();
+    if (typeof this.global.TextEncoder === 'undefined') {
+      const { TextEncoder, TextDecoder } = require('util');
+      this.global.TextEncoder = TextEncoder;
+      this.global.TextDecoder = TextDecoder;
+    }
+  }
+};

packages/gatsby/package.json

@@ -76,7 +76,7 @@
       "ts",
       "tsx"
     ],
-    "testEnvironment": "jsdom",
+    "testEnvironment": "../../.jest/dom-environment",
     "testMatch": [
       "**/*.test.ts",
       "**/*.test.tsx"

packages/react/package.json

@@ -90,7 +90,7 @@
       "ts",
       "tsx"
     ],
-    "testEnvironment": "jsdom",
+    "testEnvironment": "../../.jest/dom-environment",
     "testMatch": [
       "**/*.test.ts",
       "**/*.test.tsx"