add another test to check overrides and presidence, update the restoring of process.env the proper way

Author: Anmol1696

packages/smtppostmaster/__tests__/send.test.ts

@@ -2,12 +2,18 @@ import { send, resetTransport } from '../src/index';
 import { createSmtpCatcher } from './smtp-catcher';
 
 describe('send', () => {
-  const originalEnv = { ...process.env };
+  const ORIGINAL_ENV = { ...process.env };
 
   afterEach(() => {
     resetTransport();
-    // Restore original env vars
-    process.env = { ...originalEnv };
+    // Remove any env var added during the test
+    for (const key of Object.keys(process.env)) {
+      if (!(key in ORIGINAL_ENV)) {
+        delete process.env[key];
+      }
+    }
+    // Restore original values
+    Object.assign(process.env, ORIGINAL_ENV);
   });
 
   it('sends email via SMTP catcher with overrides', async () => {
@@ -67,4 +73,44 @@ describe('send', () => {
       await catcher.stop();
     }
   }, 10000);
+
+  it('overrides take precedence over environment variables', async () => {
+    const catcher = await createSmtpCatcher();
+
+    // Set env vars with WRONG port - would fail if used
+    process.env.SMTP_HOST = '127.0.0.1';
+    process.env.SMTP_PORT = '59999';
+    process.env.SMTP_SECURE = 'false';
+    process.env.SMTP_FROM = 'env-sender@example.com';
+
+    // Clear cached transport
+    resetTransport();
+
+    try {
+      // Send with overrides - should use overrides (correct port), not env vars
+      await send(
+        {
+          to: 'recipient@example.com',
+          subject: 'Override test',
+          text: 'This email should use override config, not env.'
+        },
+        {
+          host: catcher.host,
+          port: catcher.port, // Correct port from catcher
+          secure: false,
+          from: 'override-sender@example.com',
+          tlsRejectUnauthorized: false
+        }
+      );
+
+      const message = await catcher.waitForMessage(5000);
+
+      expect(message.raw).toContain('Subject: Override test');
+      expect(message.raw).toContain('This email should use override config');
+      expect(message.raw).toContain('From: override-sender@example.com');
+      expect(message.raw).not.toContain('From: env-sender@example.com');
+    } finally {
+      await catcher.stop();
+    }
+  }, 10000);
 });