feat: Add comprehensive SMTP test suite for Deno

- Implemented SMTP client utilities in `test/helpers/smtp.client.ts` for creating test clients, sending emails, and testing connections.
- Developed SMTP protocol test utilities in `test/helpers/utils.ts` for managing TCP connections, sending commands, and handling responses.
- Created a detailed README in `test/readme.md` outlining the test framework, infrastructure, organization, and running instructions.
- Ported CMD-01: EHLO Command tests in `test/suite/smtpserver_commands/test.cmd-01.ehlo-command.test.ts` with multiple scenarios including valid and invalid hostnames.
- Ported CMD-02: MAIL FROM Command tests in `test/suite/smtpserver_commands/test.cmd-02.mail-from.test.ts` covering valid address acceptance, invalid address rejection, SIZE parameter support, and command sequence enforcement.

test/suite/smtpserver_commands/test.cmd-02.mail-from.test.ts

@@ -0,0 +1,169 @@
+/**
+ * CMD-02: MAIL FROM Command Tests
+ * Tests SMTP MAIL FROM command validation and handling
+ */
+
+import { assert, assertMatch } from '@std/assert';
+import { startTestServer, stopTestServer, type ITestServer } from '../../helpers/server.loader.ts';
+import {
+  connectToSmtp,
+  waitForGreeting,
+  sendSmtpCommand,
+  closeSmtpConnection,
+} from '../../helpers/utils.ts';
+
+const TEST_PORT = 25252;
+let testServer: ITestServer;
+
+Deno.test({
+  name: 'CMD-02: Setup - Start SMTP server',
+  async fn() {
+    testServer = await startTestServer({ port: TEST_PORT });
+    assert(testServer, 'Test server should be created');
+  },
+  sanitizeResources: false,
+  sanitizeOps: false,
+});
+
+Deno.test({
+  name: 'CMD-02: MAIL FROM - accepts valid sender addresses',
+  async fn() {
+    const conn = await connectToSmtp('localhost', TEST_PORT);
+
+    try {
+      await waitForGreeting(conn);
+      await sendSmtpCommand(conn, 'EHLO test.example.com', '250');
+
+      const validAddresses = [
+        'sender@example.com',
+        'test.user+tag@example.com',
+        'user@[192.168.1.1]',  // IP literal
+        'user@subdomain.example.com',
+        'user@very-long-domain-name-that-is-still-valid.example.com',
+        'test_user@example.com',  // underscore in local part
+      ];
+
+      for (const address of validAddresses) {
+        console.log(`✓ Testing valid address: ${address}`);
+        const response = await sendSmtpCommand(conn, `MAIL FROM:<${address}>`, '250');
+        assert(response.startsWith('250'), `Should accept valid address: ${address}`);
+
+        // Reset for next test
+        await sendSmtpCommand(conn, 'RSET', '250');
+      }
+    } finally {
+      await closeSmtpConnection(conn);
+    }
+  },
+  sanitizeResources: false,
+  sanitizeOps: false,
+});
+
+Deno.test({
+  name: 'CMD-02: MAIL FROM - rejects invalid sender addresses',
+  async fn() {
+    const conn = await connectToSmtp('localhost', TEST_PORT);
+
+    try {
+      await waitForGreeting(conn);
+      await sendSmtpCommand(conn, 'EHLO test.example.com', '250');
+
+      const invalidAddresses = [
+        'notanemail',               // No @ symbol
+        '@example.com',             // Missing local part
+        'user@',                    // Missing domain
+        'user@.com',                // Invalid domain
+        'user@domain..com',         // Double dot
+        'user space@example.com',   // Space in address
+      ];
+
+      for (const address of invalidAddresses) {
+        console.log(`✗ Testing invalid address: ${address}`);
+        try {
+          const response = await sendSmtpCommand(conn, `MAIL FROM:<${address}>`);
+          // Should get 5xx error
+          assertMatch(response, /^5\d\d/, `Should reject invalid address with 5xx: ${address}`);
+        } catch (error) {
+          // Connection might be dropped for really bad input, which is acceptable
+          console.log(`  Address "${address}" caused error (acceptable):`, error.message);
+        }
+
+        // Try to reset (may fail if connection dropped)
+        try {
+          await sendSmtpCommand(conn, 'RSET', '250');
+        } catch {
+          // Reset after connection closed, reconnect for next test
+          conn.close();
+          return; // Exit test early if connection was dropped
+        }
+      }
+    } finally {
+      try {
+        await closeSmtpConnection(conn);
+      } catch {
+        // Ignore errors if connection already closed
+      }
+    }
+  },
+  sanitizeResources: false,
+  sanitizeOps: false,
+});
+
+Deno.test({
+  name: 'CMD-02: MAIL FROM - supports SIZE parameter',
+  async fn() {
+    const conn = await connectToSmtp('localhost', TEST_PORT);
+
+    try {
+      await waitForGreeting(conn);
+      const caps = await sendSmtpCommand(conn, 'EHLO test.example.com', '250');
+
+      // Verify SIZE is advertised
+      assert(caps.includes('SIZE'), 'Server should advertise SIZE capability');
+
+      // Try MAIL FROM with SIZE parameter
+      const response = await sendSmtpCommand(
+        conn,
+        'MAIL FROM:<sender@example.com> SIZE=5000',
+        '250'
+      );
+      assert(response.startsWith('250'), 'Should accept SIZE parameter');
+    } finally {
+      await closeSmtpConnection(conn);
+    }
+  },
+  sanitizeResources: false,
+  sanitizeOps: false,
+});
+
+Deno.test({
+  name: 'CMD-02: MAIL FROM - enforces correct sequence',
+  async fn() {
+    const conn = await connectToSmtp('localhost', TEST_PORT);
+
+    try {
+      await waitForGreeting(conn);
+
+      // Try MAIL FROM before EHLO - should fail
+      const response = await sendSmtpCommand(conn, 'MAIL FROM:<sender@example.com>');
+      assertMatch(response, /^5\d\d/, 'Should reject MAIL FROM before EHLO/HELO');
+    } finally {
+      try {
+        conn.close();
+      } catch {
+        // Ignore close errors
+      }
+    }
+  },
+  sanitizeResources: false,
+  sanitizeOps: false,
+});
+
+Deno.test({
+  name: 'CMD-02: Cleanup - Stop SMTP server',
+  async fn() {
+    await stopTestServer(testServer);
+  },
+  sanitizeResources: false,
+  sanitizeOps: false,
+});