Replace NodeJS dict aliases with maps and named field reads

Co-authored-by: Danny Kim <temeddix@gmail.com>
Co-committed-by: Danny Kim <temeddix@gmail.com>

src/testing/index.ts

@@ -1,12 +1,12 @@
-// Test support: the current user's IDs, a fresh temporary directory, and a
-// plain command runner. It imports no source module, so the repository-level
-// tests in tests/, which reach src/ only through `#testing`, never touch
-// internals.
+// Test support: the current user's IDs, a fresh temporary directory, the
+// inherited environment, and a plain command runner. It imports no source
+// module, so the repository-level tests in tests/, which reach src/ only
+// through `#testing`, never touch internals.
 import { spawn } from "node:child_process";
 import { once } from "node:events";
 import { mkdtemp } from "node:fs/promises";
 import { tmpdir } from "node:os";
-import { join } from "node:path";
+import nodePath from "node:path";
 import process from "node:process";
 import { text } from "node:stream/consumers";
 
@@ -24,8 +24,9 @@ export const IS_ROOT: boolean = currentUid() === 0;
 // Symlinks and POSIX modes, as these tests use them, need a Unix host.
 export const IS_WINDOWS: boolean = process.platform === "win32";
 
-export function makeTempDir(): Promise<string> {
-  return mkdtemp(join(tmpdir(), "bot-agents-test-"));
+export async function makeTempDir(): Promise<string> {
+  const path = await mkdtemp(nodePath.join(tmpdir(), "bot-agents-test-"));
+  return path;
 }
 
 export interface CommandResult {
@@ -33,15 +34,32 @@ export interface CommandResult {
   stderr: string;
 }
 
+// This process's environment as a map from variable name to value.
+export function inheritedEnvironment(): Map<string, string> {
+  const result = new Map<string, string>();
+  for (const [name, value] of Object.entries(process.env)) {
+    if (value !== undefined) {
+      result.set(name, value);
+    }
+  }
+  return result;
+}
+
 // Runs a command with stdin closed and only the given environment, and
 // collects its stderr.
 export async function runCommand(
   command: string,
   args: string[],
-  env: NodeJS.ProcessEnv,
+  env: ReadonlyMap<string, string>,
 ): Promise<CommandResult> {
-  const child = spawn(command, args, { env, stdio: ["ignore", "ignore", "pipe"] });
-  const [stderr, closed] = await Promise.all([text(child.stderr), once(child, "close")]);
+  const child = spawn(command, args, {
+    env: Object.fromEntries(env),
+    stdio: ["ignore", "ignore", "pipe"],
+  });
+  const [stderr, closed] = await Promise.all([
+    text(child.stderr),
+    once(child, "close"),
+  ]);
   const exitCode: unknown = closed[0];
   return { success: exitCode === 0, stderr };
 }