```ruby
require 'test_helper'
require "fixtures/sample_mail"

class MailFormTest < ActiveSupport::TestCase
  test "sample mail has name and email as attributes" do
    sample = SampleMail.new
    sample.name = "User"
    assert_equal "User", sample.name
    sample.email = "user@example.com"
    assert_equal "user@example.com", sample.email
  end
end
```

Add test 'sample mail can clear attributes using clear_prefix'
user
```ruby
require 'test_helper'
require "fixtures/sample_mail"

class MailFormTest < ActiveSupport::TestCase
  test "sample mail has name and email as attributes" do
    sample = SampleMail.new
    sample.name = "User"
    assert_equal "User", sample.name
    sample.email = "user@example.com"
    assert_equal "user@example.com", sample.email
  end
  test "sample mail can clear attributes using clear_prefix" do 
  	sample = SampleMail.new
  	sample.name = "User"
  	sample.email = "user@example.com"
  	assert_equal "User", sample.name
  	assert_equal "user@example.com", sample.email

  	sample.clear_name
  	sample.clear_email
  	assert_nil sample.name
  	assert_nil sample.email
  end
end
```
assistant