diff --git a/src/client/cross-spawn.test.ts b/src/client/cross-spawn.test.ts
index 724ec706..8480d94f 100644
--- a/src/client/cross-spawn.test.ts
+++ b/src/client/cross-spawn.test.ts
@@ -1,4 +1,4 @@
-import { getDefaultEnvironment, StdioClientTransport } from "./stdio.js";
+import { StdioClientTransport, getDefaultEnvironment } from "./stdio.js";
 import spawn from "cross-spawn";
 import { JSONRPCMessage } from "../types.js";
 import { ChildProcess } from "node:child_process";
@@ -67,19 +67,37 @@ describe("StdioClientTransport using cross-spawn", () => {
 
     await transport.start();
 
-    // verify environment variables are passed correctly
+    // verify environment variables are merged correctly
     expect(mockSpawn).toHaveBeenCalledWith(
       "test-command",
       [],
       expect.objectContaining({
         env: {
           ...getDefaultEnvironment(),
-          ...customEnv,
+          ...customEnv
         }
       })
     );
   });
 
+  test("should use default environment when env is undefined", async () => {
+    const transport = new StdioClientTransport({
+      command: "test-command",
+      env: undefined
+    });
+
+    await transport.start();
+
+    // verify default environment is used
+    expect(mockSpawn).toHaveBeenCalledWith(
+      "test-command",
+      [],
+      expect.objectContaining({
+        env: getDefaultEnvironment()
+      })
+    );
+  });
+
   test("should send messages correctly", async () => {
     const transport = new StdioClientTransport({
       command: "test-command"
diff --git a/src/client/stdio.test.ts b/src/client/stdio.test.ts
index 3d76a819..b2132446 100644
--- a/src/client/stdio.test.ts
+++ b/src/client/stdio.test.ts
@@ -1,24 +1,10 @@
 import { JSONRPCMessage } from "../types.js";
-import { StdioClientTransport, StdioServerParameters, DEFAULT_INHERITED_ENV_VARS, getDefaultEnvironment } from "./stdio.js";
-import { AsyncLocalStorage } from "node:async_hooks";
+import { StdioClientTransport, StdioServerParameters } from "./stdio.js";
 
 const serverParameters: StdioServerParameters = {
   command: "/usr/bin/tee",
 };
 
-const envAsyncLocalStorage = new AsyncLocalStorage<{ env: Record<string, string> }>();
-
-jest.mock('cross-spawn', () => {
-  const originalSpawn = jest.requireActual('cross-spawn');
-  return jest.fn((command, args, options) => {
-    const env = envAsyncLocalStorage.getStore();
-    if (env) {
-      env.env = options.env;
-    }
-    return originalSpawn(command, args, options);
-  });
-});
-
 test("should start then close cleanly", async () => {
   const client = new StdioClientTransport(serverParameters);
   client.onerror = (error) => {
@@ -74,68 +60,11 @@ test("should read messages", async () => {
   await client.close();
 });
 
-
-test("should properly set default environment variables in spawned process", async () => {
-  await envAsyncLocalStorage.run({ env: {} }, async () => {
+test("should return child process pid", async () => {
   const client = new StdioClientTransport(serverParameters);
 
   await client.start();
+  expect(client.pid).not.toBeNull();
   await client.close();
-
-  // Get the default environment variables
-  const defaultEnv = getDefaultEnvironment();
-  const spawnEnv = envAsyncLocalStorage.getStore()?.env;
-  expect(spawnEnv).toBeDefined();
-  // Verify that all default environment variables are present
-  for (const key of DEFAULT_INHERITED_ENV_VARS) {
-    if (process.env[key] && !process.env[key].startsWith("()")) {
-      expect(spawnEnv).toHaveProperty(key);
-      expect(spawnEnv![key]).toBe(process.env[key]);
-        expect(spawnEnv![key]).toBe(defaultEnv[key]);
-      }
-    }
-  });
-});
-
-test("should override default environment variables with custom ones", async () => {
-  await envAsyncLocalStorage.run({ env: {} }, async () => {
-  const customEnv = {
-    HOME: "/custom/home",
-    PATH: "/custom/path",
-    USER: "custom_user"
-  };
-
-  const client = new StdioClientTransport({
-    ...serverParameters,
-    env: customEnv
-  });
-
-  await client.start();
-  await client.close();
-  
-  const spawnEnv = envAsyncLocalStorage.getStore()?.env;
-  expect(spawnEnv).toBeDefined();
-  // Verify that custom environment variables override default ones
-  for (const [key, value] of Object.entries(customEnv)) {
-    expect(spawnEnv).toHaveProperty(key);
-    expect(spawnEnv![key]).toBe(value);
-  }
-
-  // Verify that other default environment variables are still present
-  for (const key of DEFAULT_INHERITED_ENV_VARS) {
-    if (!(key in customEnv) && process.env[key] && !process.env[key].startsWith("()")) {
-      expect(spawnEnv).toHaveProperty(key);
-      expect(spawnEnv![key]).toBe(process.env[key]);
-    }
-    }
-  });
-
-  test("should return child process pid", async () => {
-    const client = new StdioClientTransport(serverParameters);
-
-    await client.start();
-    expect(client.pid).not.toBeNull();
-    await client.close();
-    expect(client.pid).toBeNull();
-  });
+  expect(client.pid).toBeNull();
 });