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

# Why impose restrictions?

A common trait of all default generators is that they’re pretty broad in the data they generate, and from time to time, we’ll want to exclude specific counterexamples. In fact, we already needed to do that when we used the `non_empty()` generator to remove empty lists or binaries from the generated data set. Such a filter generator can be implemented with the `?SUCHTHAT(InstanceOfType, TypeGenerator, BooleanExp)` macro.

# The `?SUCHTHAT` macro

The macro works in a similar manner as `?LET`. The `TypeGenerator` is bound to `InstanceOfType`, which can then be used in `BooleanExp`. However, unlike `?SUCHTHAT` macros, `?LET` requires that `BooleanExp`  be a boolean expression, returning `true` or `false`. If the value is `true`, the data generated is kept and allowed to go through. If the value is `false`, the data is prevented from being passed to the test. The `non_empty()` filter can in fact be implemented as the following code:

Learn the importance of imposing restrictions and their advantages over transformations.

Imposing Restrictions

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

Imposing Restrictions

Why impose restrictions?

The `?SUCHTHAT` macro

Imposing Restrictions

Why impose restrictions?

The ?SUCHTHAT macro

The `?SUCHTHAT` macro