[LRUG] Testing PDFs

[Josh McMillan]

I'm currently writing a bunch of smoke tests that involve checking the
validity of machine generated PDFs. We use a multi-layer approach depending
on how fast we want the suite to run:

   - Basic tests for the content in the document – checking the right text
   boxes etc are rendered in the right place. This is done with Prawn's
   pdf-inspector package: https://github.com/prawnpdf/pdf-inspector
   - Pixel-by-pixel comparison tests using ImageMagick (the `convert` tool
   can handle PDFs as if it they were images) with a level of tolerance:
   https://www.imagemagick.org/script/compare.php

In the event that there's a major difference between two PDFs as flagged by
ImageMagick, we output a load of visual diffs (which can be done via
`compare -verbose -metric RMSE -highlight-color <actual> <expected>
<diff>`, see the above link) for validation by a human.

The validity of these PDFs is "mission critical" though (they get printed
and sent to customers as a physical product that they've paid money for) so
this is probably overkill for most scenarios.

On Tue, Aug 1, 2017 at 8:29 PM, Mark Burns <markthedeveloper at gmail.com>
wrote:

> Yeah that's the kind of thing I was thinking.
>
> I guess I may have been a bit too hopeful. No magical silver bullet
> shortcuts.
>
> Just about getting as close as possible to automating the actual
> eyeballing of the doc.
>
> diff-pdf sounded promising then:
>
> ```
> $ diff-pdf book-1.pdf book-2.pdf
> $ diff-pdf book-1.pdf book-2.pdf --verbose
> page 1 differs
> page 4 differs
> ```
>
> Much better than nothing though :)
>
> On Tue, Aug 1, 2017 at 8:21 PM Gerhard Lazu <gerhard at lazu.co.uk> wrote:
>
>> A visual diff sounds most reasonable. Never used it myself, but
>> https://github.com/vslavik/diff-pdf is worth a try. And guess what? brew
>> install diff-pdf
>>
>> On Tue, Aug 1, 2017 at 8:00 PM, Mark Burns <markthedeveloper at gmail.com>
>> wrote:
>>
>>> Has anyone any recommendations or suggestions for testing PDF generation?
>>>
>>> I'm working on a side project and using Prawn. Which is great. I can
>>> programmatically generate large aspects of the content I want.
>>>
>>> But so far I've been tweaking then looking at the result in the browser.
>>> It's not an absolute nightmare - a few seconds to render. But it's hard
>>> to know whether the result is working without actually looking at it.
>>>
>>> The DSL is nice, but very imperative. Mocking method calls out would be
>>> insane.
>>>
>>> I'm managing to refactor into small objects to represent the components
>>> and layout, pages, typography aspects etc of the document. Which brings the
>>> complexity back down to manageable chunks.
>>>
>>> But ultimately everything just calls underlying prawn DSL methods. So I
>>> can test little bits of logic that I have in my objects, but ultimately
>>> whether it works or not comes down to "have a look and see".
>>>
>>> Perhaps the best I can hope for is screenshotting when I'm happy and
>>> using approvals to verify each major change hasn't radically borked
>>> everything.
>>>
>>> It seems like there are tools to test which strings get into the
>>> document, but that seems like the easiest part. And probably the only part
>>> I'd be happy with test doubles for prawn and setting expectations on the
>>> text generating methods.
>>>
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