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

# Introduction
Property-based testing requires us to approach testing differently from what we’re used to. As we’ve seen earlier, the core of properties is coming up with rules about a program that should always remain true. That’s the hard part. But just having that will not be enough. We’ll need to find a way to turn these rules into executable code so that a specific framework (PropEr in our case) can exercise them. We will also need to tell the framework about what kind of inputs it should generate to truly challenge the rules, something we call a __generator__. Once we take the rules encoded as code, the generators, and then put them together through the framework, we have a property.

## Types of properties
Properties come in multiple varieties, but the two main categories of properties are:

1. Stateless properties
2. Stateful properties

In traditional example-based testing, it’s usually a good idea to start with simple unit tests. In property-based testing, stateless properties are their equivalent. **Stateless properties** are a great fit to validate isolated, stateless components without major side effects. They are still used for more complex stateful integration and system tests, but **stateful properties** are more appropriate for those use cases.

The properties we’ve seen and discussed in the previous chapter were all stateless, albeit a bit abstract. In this chapter, we’ll make everything concrete and see how stateless properties are structured so that we can read and understand them. We’ll also see what data generators are offered out of the box by PropEr, with some ways of composing them together. Finally, we’ll run some more properties. This will allow us to figure out how to read the results of failing test cases and see how to fix them.


Get started with properties and a better understanding of how they work to write them easily.

Introduction to 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

Introduction to Writing Properties

Introduction