rustkas

rustkas

Property-Based Testing with PropEr, Erlang, and Elixir: Finding a simplified case of inconsistency (page 146)

I noticed that the necessary inconsistence, which describes in an example PropEr framework does not find a discrepancy in the RFC 4180 specification, is far from at once. I was surprised when I ran the property several times and didn’t get the error I was looking for.

$ rebar3 proper
===> Testing prop_csv:prop_roundtrip()
....................................................................................................
OK: Passed 100 test(s).
===>
1/1 properties passed

When I increased the number of tests to 1000, the framework reproduced the necessary use case.

$ rebar3 proper -n 1000
===> Testing prop_csv:prop_roundtrip()
..........................!
Failed: After 27 test(s).
[#{[40,36] => []},#{[40,36] => []}]

Shrinking .......(7 time(s))
[#{[66,65] => []},#{[66,65] => []}]
===>
0/1 properties passed, 1 failed
===> Failed test cases:
prop_csv:prop_roundtrip() -> false

PropEr can help us in it better. As we know about a possible problem we can narrow Size to 1. For this task we can add simplified generator and property-based test:

%%%%%%%%%%%%%%%%%%
%%% Properties %%%
%%%%%%%%%%%%%%%%%%
prop_roundtrip_01() ->
    ?FORALL(Maps,
            csv_source_01(),
            Maps
            =:= bday_csv:decode(
                    bday_csv:encode(Maps))).

%%%%%%%%%%%%%%%%%%
%%% Generators %%%
%%%%%%%%%%%%%%%%%%

csv_source_01() ->
    ?LET(Keys, header(1), list(entry(1, Keys))).

Launching that property we get the expected error has gotten every time:

$ rebar3 proper -d apps/bday/test -p prop_roundtrip_01
===> Linking _build/default/plugins/rebar3_format to _build/test/plugins/rebar3_format
===> Linking _build/default/plugins/katana_code to _build/test/plugins/katana_code
===> Verifying dependencies...
===> Linking _build/default/plugins/covertool to _build/test/plugins/covertool
===> Compiling bday
===> Testing prop_csv:prop_roundtrip_01()
.......!
Failed: After 8 test(s).
[#{[125] => [75,85,50]},#{[125] => []},#{[125] => []}]

Shrinking ......(6 time(s))
[#{[65] => []},#{[65] => []}]
===>
0/1 properties passed, 1 failed
===> Failed test cases:
prop_csv:prop_roundtrip_01() -> false

Where Next?

Popular Pragmatic Bookshelf topics Top

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
AleksandrKudashkin
On the page xv there is an instruction to run bin/setup from the main folder. I downloaded the source code today (12/03/21) and can’t see...
New
alanq
This isn’t directly about the book contents so maybe not the right forum…but in some of the code apps (e.g. turbo/06) it sends a TURBO_ST...
New
Chrichton
Dear Sophie. I tried to do the “Authorization” exercise and have two questions: When trying to plug in an email-service, I found the ...
New
jskubick
I think I might have found a problem involving SwitchCompat, thumbTint, and trackTint. As entered, the SwitchCompat changes color to hol...
New
brunogirin
When trying to run tox in parallel as explained on page 151, I got the following error: tox: error: argument -p/–parallel: expected one...
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
s2k
Hi all, currently I wonder how the Tailwind colours work (or don’t work). For example, in app/views/layouts/application.html.erb I have...
New
EdBorn
Title: Agile Web Development with Rails 7: (page 70) I am running windows 11 pro with rails 7.0.3 and ruby 3.1.2p20 (2022-04-12 revision...
New
gorkaio
root_layout: {PentoWeb.LayoutView, :root}, This results in the following following error: no “root” html template defined for PentoWeb...
New

Other popular topics Top

AstonJ
A thread that every forum needs! Simply post a link to a track on YouTube (or SoundCloud or Vimeo amongst others!) on a separate line an...
New
PragmaticBookshelf
Write Elixir tests that you can be proud of. Dive into Elixir’s test philosophy and gain mastery over the terminology and concepts that u...
New
DevotionGeo
I know that -t flag is used along with -i flag for getting an interactive shell. But I cannot digest what the man page for docker run com...
New
AstonJ
If you are experiencing Rails console using 100% CPU on your dev machine, then updating your development and test gems might fix the issu...
New
PragmaticBookshelf
Create efficient, elegant software tests in pytest, Python's most powerful testing framework. Brian Okken @brianokken Edited by Kat...
New
PragmaticBookshelf
Build efficient applications that exploit the unique benefits of a pure functional language, learning from an engineer who uses Haskell t...
New
PragmaticBookshelf
Author Spotlight Jamis Buck @jamis This month, we have the pleasure of spotlighting author Jamis Buck, who has written Mazes for Prog...
New
PragmaticBookshelf
Author Spotlight Rebecca Skinner @RebeccaSkinner Welcome to our latest author spotlight, where we sit down with Rebecca Skinner, auth...
New
New
NewsBot
Node.js v22.14.0 has been released. Link: Release 2025-02-11, Version 22.14.0 'Jod' (LTS), @aduh95 · nodejs/node · GitHub
New

Sub Categories: