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

# The application 
The application will be a bookstore implementation that uses a PostgreSQL back-end, with SQL queries and network connections as part of the code to be tested. Even with all these moving pieces, we’ll still be able to test it all using Elixir.

Because real-world systems contain more moving parts, they’ll have a far larger portfolio of errors and strange behaviors to detect and debug. We’ll keep on using stateful properties, but we may have to adjust our strategy a bit to make our lives easier.

Like many other system tests, we’ll start with a prewritten system, and mainly focus on testing it. The base system will use a few open source libraries, mostly around interacting with a database.

The first big dependency for this chapter is going to be an install of PostgreSQL, at version 9.6 or above.

# Setting up the application

Get introduced to the bookstore application, and the database initialization script.

Introducing the Application

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

Introducing the Application

The application