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

# Execution of stateful properties

PropEr divides the execution of a stateful test into two phases, one abstract and one real. The abstract phase is used to create a test scenario and is executed without any code from our actual system running. Its whole objective is to take the model and command generation callbacks and call these to build out the sequence of calls that will later be applied to the system.

Put visually, it looks like this:

> Note the lack of postcondition or calls to the actual system.

In the abstract mode, a command generator creates a symbolic call with its arguments based on an initial model state. PropEr then applies the preconditions to that command to know if it would be valid. If the validation fails, PropEr tries again with a new generated command. Once a suitable command is found, we can move forward. The `next_state` function takes the command and the current state and has to return a new state data structure. Then the whole process is repeated over and over until PropEr decides it has enough commands.

Once this is done, we’re left with a valid and legitimate sequence of commands, with all its expected state transitions. After that, our model is ready. 

With our model in hand, PropEr can start applying the commands to the real system, and our postconditions can check that things all remain valid as shown in the diagram below:



Understand how stateful properties are executed and how the execution flow works.


How Stateful Properties Run

Understand how stateful properties are executed and how the execution flow works.

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

How Stateful Properties Run

Execution of stateful properties