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 application

The application just starts a standard supervisor without children. This is how it's done.

```erlang
-module(bookstore_app).
-behaviour(application).

%% Application callbacks
-export([start/2, stop/1]).

start(_StartType, _StartArgs) ->
    bookstore_sup:start_link().

stop(_State) ->
    ok.
```

And now for the supervisor. Let's look at how that works. 

# The supervisor

This is what our supervisor would look like. 

```erlang
-module(bookstore_sup).
-behaviour(supervisor).

-export([start_link/0]).
-export([init/1]).

start_link() ->
    supervisor:start_link({local, ?MODULE}, ?MODULE, []).

init([]) ->
    bookstore_db:load_queries(),
    {ok, {{one_for_all, 0, 1}, []}}.
```

Note that `bookstore_db:load_queries()` gets called. This function is not yet defined. Its role, though, will be to find all the SQL queries within a file we’ll define in `priv/queries.sql`, which are labeled by name in the comments.

# Queries

Take a look at the basics of the application, what it does, and the SQL queries that the application will be using.

The Application: Getting Started

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

The Application: Getting Started

The application