Add comprehensive SMTP command tests for RCPT TO, DATA, QUIT, TLS, and basic email sending

- Implement CMD-03 tests for RCPT TO command, validating recipient addresses, handling multiple recipients, and enforcing command sequence.
- Implement CMD-04 tests for DATA command, ensuring proper email content transmission, handling of dot-stuffing, large messages, and correct command sequence.
- Implement CMD-13 tests for QUIT command, verifying graceful connection termination and idempotency.
- Implement CM-01 tests for TLS connections, including STARTTLS capability and direct TLS connections.
- Implement EP-01 tests for basic email sending, covering complete SMTP transaction flow, MIME attachments, HTML emails, custom headers, and minimal emails.

test/helpers/utils.ts

@@ -87,19 +87,13 @@ async function readWithTimeout(
 }
 
 /**
- * Send SMTP command and wait for response
+ * Read SMTP response without sending a command
  */
-export async function sendSmtpCommand(
+export async function readSmtpResponse(
   conn: Deno.TcpConn,
-  command: string,
   expectedCode?: string,
   timeout: number = 5000
 ): Promise<string> {
-  // Send command
-  const encoder = new TextEncoder();
-  await conn.write(encoder.encode(command + '\r\n'));
-
-  // Read response
   let buffer = '';
   const startTime = Date.now();
 
@@ -116,7 +110,24 @@ export async function sendSmtpCommand(
     }
   }
 
-  throw new Error(`Command timeout after ${timeout}ms`);
+  throw new Error(`Response timeout after ${timeout}ms`);
+}
+
+/**
+ * Send SMTP command and wait for response
+ */
+export async function sendSmtpCommand(
+  conn: Deno.TcpConn,
+  command: string,
+  expectedCode?: string,
+  timeout: number = 5000
+): Promise<string> {
+  // Send command
+  const encoder = new TextEncoder();
+  await conn.write(encoder.encode(command + '\r\n'));
+
+  // Read response using the dedicated function
+  return await readSmtpResponse(conn, expectedCode, timeout);
 }
 
 /**