Gain insights into property-based testing with PropEr in Erlang. Delve into foundational principles, common frameworks, custom data generators, and applying testing in realistic projects for robust code validation.

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Property-based testing relies on specifying some property of code, rather than unit tests which specify the expected output in response to some inputs. In this course, you’ll cover the concepts you need to get started, up to the point where you feel confident enough to use the most advanced features of PropEr with Erlang.

You’ll start smoothly with the basic and foundational principles of property-based testing. From there, you will cover some of the common frameworks, how to think in properties, how to write your own custom data generators, and more. You'll also see how you can use Property-Based Testing in a realistic project.

By the time you finish this course, you will be comfortable testing real-world applications using properties.

Property-Based Testing with PropEr in Erlang

Which of the following macros is used for shrinking?

Which of the following macros is used for shrinking?

`?LETSHRINK` always takes a list of arguments and generators, whereas `?LET` takes any pattern and any generator into its first two arguments.

A `?LET` macro has rules to apply specific transformations.


One of the generators in the list will be used, but without the transformations being applied in the `?LETSHRINK` macro.

Which of the following is a difference between the `?LETSHRINK` macro and the `?LET` macro?

Which of the following is a difference between the <code>?LETSHRINK</code> macro and the <code>?LET</code> macro?

The generator provides a list but the property expects atoms.

The property expects a list coming out of the generator, but the generator is providing atoms.

The code should work and the fail cases will provide enough information about the problem.

In the following property, a list of servings for a meal is generated. If any serving contains dairy, the property fails. The property and generator are as follows:

```erlang
prop_too_much_dairy() ->
 ?FORALL(Food, meal(), dairy_count(Food) =:= 0).

dairy_count(L) ->
 length([X || X <- L, is_dairy(X)]).

is_dairy(cheesesticks) -> true;
is_dairy(lasagna) -> true;
is_dairy(icecream) -> true;
is_dairy(milk) -> true;
is_dairy(_) -> false.

meal() ->
 ?LETSHRINK([Appetizer, Drink, Entree, Dessert],
 [elements([soup, salad, cheesesticks]),
 elements([coffee, tea, milk, water, juice]),
 elements([lasagna, tofu, steak]),
 elements([cake, chocolate, icecream])],
 [Appetizer, Drink, Entree, Dessert]).
```

But whenever the test case fails, we instead get a result set that always contains the four courses. What could be a possible problem?

In the following property, a list of servings for a meal is generated. If any serving contains dairy, the property fails. The property and generator are as follows:
<pre><code class="language-erlang">prop_too_much_dairy() -&gt;
 ?FORALL(Food, meal(), dairy_count(Food) =:= 0).

dairy_count(L) -&gt;
 length([X || X &lt;- L, is_dairy(X)]).

is_dairy(cheesesticks) -&gt; true;
is_dairy(lasagna) -&gt; true;
is_dairy(icecream) -&gt; true;
is_dairy(milk) -&gt; true;
is_dairy(_) -&gt; false.

meal() -&gt;
 ?LETSHRINK([Appetizer, Drink, Entree, Dessert],
 [elements([soup, salad, cheesesticks]),
 elements([coffee, tea, milk, water, juice]),
 elements([lasagna, tofu, steak]),
 elements([cake, chocolate, icecream])],
 [Appetizer, Drink, Entree, Dessert]).
</code></pre>
But whenever the test case fails, we instead get a result set that always contains the four courses. What could be a possible problem?

Solve a short quiz to test your understanding of the concepts of shrinking.

Foundations of Property-Based Testing

Writing Properties

Thinking in Properties

Custom Generators

Responsible Testing

Properties-Driven Development

Shrinking

Targeted Properties

Stateful Properties

Case Study: Bookstore

State Machine Properties

Conclusion

Quiz Yourself on Shrinking