Refactor getEnvironment to pure function with DI

Remove module-level singleton cache and resetEnvironmentForTests()
escape hatch. getEnvironment() now accepts rawEnv parameter (defaults
to process.env) and runServer() takes Environment as a parameter.
Tests pass env directly instead of mutating process.env.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: tomassurin

src/index.ts

@@ -224,13 +224,7 @@ type RunServerResult = {
   close: () => Promise<void>
 }
 
-export async function runServer(): Promise<RunServerResult> {
-  let environment: Environment
-  try {
-    environment = getEnvironment()
-  } catch (e) {
-    throw new Error(`Invalid environment configuration: ${e instanceof Error ? e.message : e}`)
-  }
+export async function runServer(environment: Environment): Promise<RunServerResult> {
   const { sandboxDir } = await parseCommandLineArgs()
 
   await prepareSandbox(sandboxDir)
@@ -288,7 +282,15 @@ function isMainModule() {
 if (isMainModule()) {
   let activeServer: RunServerResult | undefined
 
-  runServer()
+  let environment: Environment
+  try {
+    environment = getEnvironment()
+  } catch (e) {
+    console.error(`Invalid environment configuration: ${e instanceof Error ? e.message : e}`)
+    process.exit(1)
+  }
+
+  runServer(environment)
     .then((result) => {
       activeServer = result
     })

src/utils/environment.ts

@@ -21,9 +21,7 @@ const RawEnvironmentSchema = z.object({
   CLIENT_ID: z.string().optional(),
 })
 
-let cachedEnvironment: Environment | undefined
-
-function parseEnvironment(rawEnv: NodeJS.ProcessEnv): Environment {
+export function getEnvironment(rawEnv: NodeJS.ProcessEnv = process.env): Environment {
   const raw = RawEnvironmentSchema.parse(rawEnv)
 
   return {
@@ -33,15 +31,3 @@ function parseEnvironment(rawEnv: NodeJS.ProcessEnv): Environment {
     clientId: raw.CLIENT_ID,
   }
 }
-
-export function getEnvironment(): Environment {
-  if (!cachedEnvironment) {
-    cachedEnvironment = parseEnvironment(process.env)
-  }
-
-  return cachedEnvironment
-}
-
-export function resetEnvironmentForTests() {
-  cachedEnvironment = undefined
-}

tests/environment.test.ts

@@ -1,77 +1,49 @@
-import { afterEach, beforeEach, describe, expect, it } from 'vitest'
-import { getEnvironment, resetEnvironmentForTests } from '../src/utils/environment.js'
+import { describe, expect, it } from 'vitest'
+import { getEnvironment } from '../src/utils/environment.js'
 
 describe('environment', () => {
-  const originalEnv = process.env
-
-  beforeEach(() => {
-    process.env = { ...originalEnv }
-    resetEnvironmentForTests()
-  })
-
-  afterEach(() => {
-    process.env = originalEnv
-    resetEnvironmentForTests()
-  })
-
   it('parses default configuration with API key', () => {
-    process.env.NUTRIENT_DWS_API_KEY = 'dws-key'
-
-    const environment = getEnvironment()
+    const environment = getEnvironment({ NUTRIENT_DWS_API_KEY: 'dws-key' })
 
     expect(environment.nutrientApiKey).toBe('dws-key')
     expect(environment.dwsApiBaseUrl).toBe('https://api.nutrient.io')
     expect(environment.authServerUrl).toBe('https://api.nutrient.io')
   })
 
   it('allows overriding DWS API base URL', () => {
-    process.env.DWS_API_BASE_URL = 'http://localhost:4000'
-
-    const environment = getEnvironment()
+    const environment = getEnvironment({ DWS_API_BASE_URL: 'http://localhost:4000' })
 
     expect(environment.dwsApiBaseUrl).toBe('http://localhost:4000')
   })
 
   it('allows overriding auth server URL', () => {
-    process.env.AUTH_SERVER_URL = 'http://localhost:4000'
-
-    const environment = getEnvironment()
+    const environment = getEnvironment({ AUTH_SERVER_URL: 'http://localhost:4000' })
 
     expect(environment.authServerUrl).toBe('http://localhost:4000')
   })
 
   it('allows setting client ID', () => {
-    process.env.CLIENT_ID = 'my-client'
-
-    const environment = getEnvironment()
+    const environment = getEnvironment({ CLIENT_ID: 'my-client' })
 
     expect(environment.clientId).toBe('my-client')
   })
 
   it('works without API key (OAuth mode)', () => {
-    delete process.env.NUTRIENT_DWS_API_KEY
-
-    const environment = getEnvironment()
+    const environment = getEnvironment({})
 
     expect(environment.nutrientApiKey).toBeUndefined()
   })
 
   it('throws when DWS_API_BASE_URL is not a valid URL', () => {
-    process.env.DWS_API_BASE_URL = 'not-a-url'
-
-    expect(() => getEnvironment()).toThrow()
+    expect(() => getEnvironment({ DWS_API_BASE_URL: 'not-a-url' })).toThrow()
   })
 
   it('rejects non-HTTPS AUTH_SERVER_URL', () => {
-    process.env.AUTH_SERVER_URL = 'http://example.com'
-
-    expect(() => getEnvironment()).toThrow(/https/)
+    expect(() => getEnvironment({ AUTH_SERVER_URL: 'http://example.com' })).toThrow(/https/)
   })
 
   it('allows http://localhost AUTH_SERVER_URL for local development', () => {
-    process.env.AUTH_SERVER_URL = 'http://localhost:4000'
-
-    const environment = getEnvironment()
+    const environment = getEnvironment({ AUTH_SERVER_URL: 'http://localhost:4000' })
 
     expect(environment.authServerUrl).toBe('http://localhost:4000')
   })