devtools: update jest config

This change updates the jest config to specify
test environments separately for unit and e2e
tests and adds the isolated modules option to
the ts-jest config to improve test startup time.

For golang/go#43361

Change-Id: I3fbfae2a42c26bd0eeb2d235dab1cced0c8701ea
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/280711
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

devtools/config/jest.config.js

@@ -2,5 +2,9 @@
 module.exports = {
   preset: 'ts-jest',
   rootDir: '../../',
-  testEnvironment: 'node',
+  globals: {
+    'ts-jest': {
+      isolatedModules: true,
+    },
+  },
 };

package.json

@@ -17,8 +17,8 @@
     "lint-css": "stylelint **/*.css",
     "license-check": "jsgl --local .",
     "test-typecheck": "tsc --noEmit",
-    "test-unit": "jest --config devtools/config/jest.config.js content",
-    "test-e2e": "jest --config devtools/config/jest.config.js e2e",
+    "test-unit": "jest --config devtools/config/jest.config.js --env=jsdom content",
+    "test-e2e": "jest --config devtools/config/jest.config.js --env=node e2e",
     "test": "run-s test-*"
   },
   "dependencies": {