A Single Programmer's Blog

Yesterday, I was coding a new set of tests for a Picture class. I wanted to introduce an on-disk cache, when the picture is public.

I already had an existing test/unit/picture_test.rb, which I extended.

The tests looked like this:

I knew this was the wrong way to go – the fixture was repeated more than once. Then, I realized that what I wanted was a new TestCase. I had already reached for my mouse to hit New File when I had a flash: what prevents me from simply adding a new class to picture_test.rb ?

class PictureTest < Test::Unit::TestCase
  def test_read_from_stringio
    ...
  end
end

<p>class PublicPictureTest < Test::Unit::TestCase
  def setup
    pict = uploaded_file(‘large.jpg’, ‘image/jpeg’, ‘somepicture.jpg’)
    @picture = Picture.build(pict)
    @picture.public = true
    assert_model_saved @picture
  end
end</p>

<pre><code>def test_picture_exists_on_disk
  assert File.exist?(@picture.cache_filename), 'file copied to disk'
end</code></pre>

<pre><code>def test_thumbnail_exists_on_disk
  assert File.exist?(@picture.cache_thumbnail), 'thumbnail copied to disk'
end</code></pre>

class PrivatePictureTest < Test::Unit::TestCase
  include PicturePathHelper

def setup
    pict = uploaded_file(‘large.jpg’, ‘image/jpeg’, ‘somepicture.jpg’)
    @picture = Picture.build(pict)
    @picture.public = false
    assert_model_saved @picture
  end

def test_picture_not_copied_to_disk_when_private
    assert !File.exist?(@picture.cache_filename),
        ‘image should not be on disk when picture is private’
  end

def test_thumbnail_not_copied_to_disk_when_private
    assert !File.exist?(@picture.cache_thumbnail),
        ‘thumbnail should not be on disk when picture is private’
  end
end

I also had another flash: is TestCase the right name ? Shouldn’t it be called TestFixture instead ? Because that is what instances of this class represent – a test fixture.

This is very much akin to Spec::Context, from RSpec.

And you see the tests ? They all respect the one assertion per test. I was quite happy with the results.

Now, I need to refactor those other instances in my test suite…

A Single Programmer's Blog

by François Beausoleil

Test fixtures and behavioral testing

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