input: Write a python function to generate an email address using the given name and domain.
  assert generate_email("John Doe", "example.com") == "john.doe@example.com"
  assert generate_email("Jane Smith", "test.org") == "jane.smith@test.org"
  assert generate_email("Alice Johnson", "mail.net") == "alice.johnson@mail.net"
output: def generate_email(name, domain):
      username = name.lower().replace(" ", ".")
      return f"{username}@{domain}"