Gain insights into property-based testing with PropEr in Elixir. Learn foundational principles, custom data generators, and advanced concepts for effective real-world application testing.

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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

# Summary
In this final chapter, we've seen how to bring stateful properties to the next level in cases where the system under test can be modeled as a finite state machine. In such cases, FSM properties represent a useful specialization mechanism that lets us generate calls and data according to the state in which the system should be. We’ve been through the data generation model (both symbolic and real) for the property and have put it all in practice through tests for Klarna’s `circuit_breaker` library. We came up with a multistate model, which proved to be ill-fitting for the actual library. We then went through the debugging steps required to fix the model and through the statistics collected in the test execution. Finally, we rebalanced the possible generated events to get better transition coverage.

# What's next

We now have all the knowledge required to use properties to find tricky bugs in all kinds of systems, from basic unit tests up to larger integration suites. We’re ready to go on and start adding better tests to our software, and improve software quality overall.

Wrapping Up

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

Wrapping Up

Summary