rustkas

rustkas

Property-Based Testing with PropEr, Erlang, and Elixir:the order of the elements in the comparison expression(page 53)

I’m wondering why you chose the following sequence in your expression:
Function under test =:= reference expression

prop_biggest() ->
    ?FORALL(List, (list(integer())),
            begin
                biggest(List) =:= lists:last(lists:sort(List))
            end).

EUnit macros using assertEqual(Expect, Expr), whehe EUnit uses the opposite order of items.

biggest_test() ->
 ?assert(5 =:= biggest([1, 2, 3, 4, 5])),
 ?assert(8 =:= biggest([3, 8, 7, -1])),
 ?assert(0 =:= biggest([0])), 
 ?assert(5 =:= biggest([-10, 5, -901])).

I understand that the order of the elements doesn’t matter. When you proposed your order, what were you guided by, what were your motives?

Marked As Solved

ferd

ferd

Author of Property-Based Testing with PropEr, LYSE, & Erlang in Anger

That’s an interesting question. I don’t think it’s a super conscious choice, but I tend to use the order of other assertion macros, where for example the format is ?assertMatch(Pattern, Expression) (this is the only one where it’s very sensitive, otherwise you just get the expected/actual order reversed in a report).

I think this, along with pattern matching generally having the assertion left-side, makes me compare that way. For example, many years ago, before people used EUnit macro in common test, the pattern for assertions would have just been Expected = lists:last(lists:sort(List)), Expected = biggest(List) and then letting the est crash if it’s wrong.

In this case, I appear to have swapped the order with what I generally use or would suggest to use, since the model should be driving the test!

Where Next?

Popular Pragmatic Bookshelf topics Top

jimschubert
In Chapter 3, the source for index introduces Config on page 31, followed by more code including tests; Config isn’t introduced until pag...
New
belgoros
Following the steps described in Chapter 6 of the book, I’m stuck with running the migration as described on page 84: bundle exec sequel...
New
yulkin
your book suggests to use Image.toByteData() to convert image to bytes, however I get the following error: "the getter ‘toByteData’ isn’t...
New
sdmoralesma
Title: Web Development with Clojure, Third Edition - migrations/create not working: p159 When I execute the command: user=> (create-...
New
joepstender
The generated iex result below should list products instead of product for the metadata. (page 67) iex> product = %Product{} %Pento....
New
swlaschin
The book has the same “Problem space/Solution space” diagram on page 18 as is on page 17. The correct Problem/Solution space diagrams ar...
New
digitalbias
Title: Build a Weather Station with Elixir and Nerves: Problem connecting to Postgres with Grafana on (page 64) If you follow the defau...
New
hazardco
On page 78 the following code appears: <%= link_to ‘Destroy’, product, class: ‘hover:underline’, method: :delete, data: { confirm...
New
creminology
Skimming ahead, much of the following is explained in Chapter 3, but new readers (like me!) will hit a roadblock in Chapter 2 with their ...
New
mert
AWDWR 7, page 152, page 153: Hello everyone, I’m a little bit lost on the hotwire part. I didn’t fully understand it. On page 152 @rub...
New

Other popular topics Top

AstonJ
What chair do you have while working… and why? Is there a ‘best’ type of chair or working position for developers?
New
AstonJ
We have a thread about the keyboards we have, but what about nice keyboards we come across that we want? If you have seen any that look n...
New
AstonJ
We’ve talked about his book briefly here but it is quickly becoming obsolete - so he’s decided to create a series of 7 podcasts, the firs...
New
PragmaticBookshelf
Author Spotlight: VM Brasseur @vmbrasseur We have a treat for you today! We turn the spotlight onto Open Source as we sit down with V...
New
PragmaticBookshelf
Author Spotlight: Tammy Coron @Paradox927 Gaming, and writing games in particular, is about passion, vision, experience, and immersio...
New
PragmaticBookshelf
Author Spotlight: Sophie DeBenedetto @SophieDeBenedetto The days of the traditional request-response web application are long gone, b...
New
AnfaengerAlex
Hello, I’m a beginner in Android development and I’m facing an issue with my project setup. In my build.gradle.kts file, I have the foll...
New
AstonJ
Curious what kind of results others are getting, I think actually prefer the 7B model to the 32B model, not only is it faster but the qua...
New
RobertRichards
Hair Salon Games for Girls Fun Girls Hair Saloon game is mainly developed for kids. This game allows users to select virtual avatars to ...
New
PragmaticBookshelf
Fight complexity and reclaim the original spirit of agility by learning to simplify how you develop software. The result: a more humane a...
New

Sub Categories: