diff --git a/docs/develop.md b/docs/develop.md
index 15ceb593..f152f8be 100644
--- a/docs/develop.md
+++ b/docs/develop.md
@@ -16,6 +16,7 @@ git clone https://github.com/<your-github-username>/clasp.git
 cd clasp
 ```
 - Install dependencies: `npm install`
+- Link-install this development version of `clasp`: `npm link`
 
 ### After Making a Change
 
diff --git a/test/README.md b/test/README.md
index b5439927..73a75185 100644
--- a/test/README.md
+++ b/test/README.md
@@ -14,6 +14,8 @@
 
 ## How to Run Tests
 
+Make sure you have completed the [development setup](/docs/develop.md#setup).
+
 1. Log in: `clasp login`
 1. Rebuild: `npm run build`
 1. Set environmental variables:
diff --git a/test/constants.ts b/test/constants.ts
index 1ba740ef..3134b172 100644
--- a/test/constants.ts
+++ b/test/constants.ts
@@ -2,6 +2,7 @@ import os from 'os';
 import path from 'path';
 
 import {ClaspToken} from '../src/dotfile.js';
+import {ClaspError} from '../src/clasp-error.js';
 import {randomString} from './functions.js';
 
 import type {OAuth2ClientOptions} from 'google-auth-library';
@@ -27,15 +28,20 @@ export const TEST_APPSSCRIPT_JSON_WITH_RUN_API = JSON.stringify({
 
 // Travis Env Variables
 export const IS_PR: boolean = process.env.CI === 'true';
-export const SCRIPT_ID: string = process.env.SCRIPT_ID ?? '';
-export const PROJECT_ID: string = process.env.PROJECT_ID ?? '';
-export const PARENT_ID: string[] = [process.env.PROJECT_ID ?? ''];
-const HOME: string = process.env.HOME ?? '';
+if (process.env.SCRIPT_ID === undefined) {
+  throw new ClaspError('Environment variable SCRIPT_ID is not defined.');
+}
+export const SCRIPT_ID: string = process.env.SCRIPT_ID;
+if (process.env.PROJECT_ID === undefined) {
+  throw new ClaspError('Environment variable PROJECT_ID is not defined.');
+}
+export const PROJECT_ID: string = process.env.PROJECT_ID;
+export const PARENT_ID: string[] = [process.env.PROJECT_ID];
 
 // Paths
 export const CLASP_PATHS = {
   clientCredsLocal: 'client_credentials.json',
-  rcGlobal: path.join(HOME, '.clasprc.json'),
+  rcGlobal: path.join(os.homedir(), '.clasprc.json'),
   rcLocal: '.clasprc.json',
   settingsLocal: '.clasp.json',
 };