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Property-based testing relies on specifying some property of code, unlike unit tests, which specify the expected output in response to some inputs. In this course, we'll cover the concepts we need to feel confident about using even the most advanced features of PropEr with Elixir.

We'll start with the basic and foundational principles of property-based testing, see what the framework offers us to get started, make our way through thinking in properties, write our own custom data generators, and then learn more advanced concepts. We'll also see how you can use property-based testing in a realistic project.

By the time we finish this course, we should feel comfortable testing real-world applications using properties.

Property-Based Testing with PropEr in Elixir

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

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

What function can we 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 `Enum.to_list(Start, Stop)` function

Implementing the `Enum.to_list(Start, Stop)` function 

Which of the following is an example of property testing?

```elixir
property "quiz writing properties: a sample" do
 forall {start, count} <- {integer(), non_neg_integer()} do
 list = Enum.to_list(start..(start + count))
 count + 1 == length(list) and increments(list) 
 end
end
def increments([head | tail]), do: increments(head, tail)
defp increments(_, []), do: true
defp increments(n, [head | tail]) when head == n + 1, do: increments(head, tail)
defp increments(_, _), do: false
```

Which of the following is an example of property testing?
<pre><code class="language-elixir">property &quot;quiz writing properties: a sample&quot; do
 forall {start, count} &lt;- {integer(), non_neg_integer()} do
 list = Enum.to_list(start..(start + count))
 count + 1 == length(list) and increments(list) 
 end
end
def increments([head | tail]), do: increments(head, tail)
defp increments(_, []), do: true
defp increments(n, [head | tail]) when head == n + 1, do: increments(head, tail)
defp increments(_, _), do: 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

Stateful Properties

Case Study: Bookstore

State Machine Properties

Conclusion

Quiz Yourself on Writing Properties