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 callbacks for stateful tests belong in the real interaction with the system but not in the abstract phase?

Which callbacks for stateful tests belong in the real interaction with the system but not in the abstract phase?

The actual system will be started and stopped before every single test iteration.

The actual system will be booted once before the tests run. The system instance will be shared for all iterations before being shut down after the whole run.

The actual system will be started, then an abstract representation of the test case will be created. After this, the system will be stopped. The test itself will not have run once at that point, so by the time the framework would try to execute the test, the actual system would have already shut down.

What happens to the system in the following property?

```erlang
prop_test() ->
    ?FORALL(Cmds, commands(?MODULE),
        begin
            actual_system:start_link(),
            {_History, _State, Result} = run_commands(?MODULE, Cmds), 
            actual_system:stop(),
            Result =:= ok
        end).
```

What happens to the system in the following property?
<pre><code class="language-erlang">prop_test() -&gt;
 ?FORALL(Cmds, commands(?MODULE),
 begin
 actual_system:start_link(),
 {_History, _State, Result} = run_commands(?MODULE, Cmds), 
 actual_system:stop(),
 Result =:= ok
 end).
</code></pre>

The actual system will be booted once before the tests run. The system instance will be shared for all iterations, before being shut down after the whole run. 

The actual system will be started, then an abstract representation of the test case will be created. After this, the system will be stopped. But the test itself will not have run once at that point, so by the time the framework would try to execute the test, the actual system would have already shut down.

What happens to the system in the following property?

```erlang
prop_test() -> 
    actual_system:start_link(), 
    ?FORALL(Cmds, commands(?MODULE),
        begin
            {_History, _State, Result} = run_commands(?MODULE, Cmds), 
            Result =:= ok
        end), 
    actual_system:stop().
```

What happens to the system in the following property?
<pre><code class="language-erlang">prop_test() -&gt; 
 actual_system:start_link(), 
 ?FORALL(Cmds, commands(?MODULE),
 begin
 {_History, _State, Result} = run_commands(?MODULE, Cmds), 
 Result =:= ok
 end), 
 actual_system:stop().
</code></pre>

Solve a short quiz to test your understanding of the concepts of stateful 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 Stateful Properties