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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

`proper_types:list(proper_types:Types())).`

What function can you call to get a sample of a generator’s data?

What function can you call to get a sample of a generator’s data?

Which of the following is present in a test file?

Which of the following is present in a test file?

Validating the `lists:seq(Start, Stop)` function

Implementing the `lists:seq(Start, Stop)` function 

What of the following is an example of testing?


```erlang
prop_a_sample() ->
    ?FORALL({Start,Count}, {integer(), non_neg_integer()},
        begin
            List = lists:seq(Start, Start+Count), Count+1 =:= length(List)
            andalso
            increments(List) 
        end).
increments([Head | Tail]) -> increments(Head, Tail).
increments(_, []) -> true;
increments(N, [Head|Tail]) when Head == N+1 -> increments(Head, Tail); increments(_, _) -> false.
```


What of the following is an example of testing?
<pre><code class="language-erlang">prop_a_sample() -&gt;
 ?FORALL({Start,Count}, {integer(), non_neg_integer()},
 begin
 List = lists:seq(Start, Start+Count), Count+1 =:= length(List)
 andalso
 increments(List) 
 end).
increments([Head | Tail]) -&gt; increments(Head, Tail).
increments(_, []) -&gt; true;
increments(N, [Head|Tail]) when Head == N+1 -&gt; increments(Head, Tail); increments(_, _) -&gt; false.
</code></pre>

Quiz on Writing Properties

Quiz on Writing Properties

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

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 Writing Properties