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

The properties we've seen so far were pseudocode-like and left a lot to the imagination. Now that we have a stand-in directory structure with a structure similar to what we'd have in a real project, we're going to tie everything together. We'll add a property to the project and execute it. The property will be basic and test nothing of significance, but it'll give us a brief idea of what things look like and how they should all fit together.

# Properties in practice
PropEr's properties are not located within the same module as our production source code. Instead, we'll enforce a strict separation of production and test codes by forcing all properties to be placed in standalone modules under the `test/` directory.

Properties must be added to modules that have a name starting with `prop_`. Besides this, they are regular Erlang codes. We can add a module named `prop_foundations` under `test/prop_foundations.erl`, or we can also use templates to do the same thing for us by calling the following command within the project's root directory:

```CLI
rebar3 new proper foundations
```

> Take a look at the created file in the code widget below


We can run the test in the code below:

> **Note:** To execute the code after changing it, please click "Run," which will save your code, and then run `rebar3 proper` in the terminal.

Running a Property

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

Running a Property