input: Write a Python function to query all users from a database and print their names and emails.
  assert query_users() == "User: John Doe, Email: john@example.com\nUser: Jane Doe, Email: jane@example.com\n"
  assert query_users() == "User: Alice, Email: alice@example.com\nUser: Bob, Email: bob@example.com\n"
output: def query_users():
      import sqlite3
  
      connection = sqlite3.connect(':memory:')  # Use an in-memory database for simplicity
      cursor = connection.cursor()
  
      # Create a table and insert some example users
      cursor.execute('CREATE TABLE users (name TEXT, email TEXT)')
      cursor.execute('INSERT INTO users (name, email) VALUES (?, ?)', ('John Doe', 'john@example.com'))
      cursor.execute('INSERT INTO users (name, email) VALUES (?, ?)', ('Jane Doe', 'jane@example.com'))
      cursor.execute('INSERT INTO users (name, email) VALUES (?, ?)', ('Alice', 'alice@example.com'))
      cursor.execute('INSERT INTO users (name, email) VALUES (?, ?)', ('Bob', 'bob@example.com'))
  
      # Fetch all users
      cursor.execute('SELECT name, email FROM users')
      users = cursor.fetchall()
  
      # Format the output
      result = ""
      for user in users:
          result += f"User: {user[0]}, Email: {user[1]}\n"
  
      connection.close()
      return result.strip()  # Remove the trailing newline
  
  # Example usage:
  # print(query_users())