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

## Adding the call back
Let's take a look at the call-backs

The call back is in the `test/break_test.exs` file in the code below between *line 78* and *line 90*. It has been highlighted.

The call raises the probability of any call forcing a transition from `ok` to `tripped` and also increases the probability of all error calls in the `ok` state. The rest of calls, such as error calls that are already in the `tripped` state and manual blocks, remain neutral in terms of probabilities.

Let's run the code and see what we get. 

## Running the code

# Adding the call back
Let's take a look at the call-backs

The call back is in the `test/break_test.exs` file in the code below between *line 78* and *line 90*. It has been highlighted.

The call raises the probability of any call forcing a transition from `ok` to `tripped` and also increases the probability of all error calls in the `ok` state. The rest of calls, such as error calls that are already in the `tripped` state and manual blocks, remain neutral in terms of probabilities.

Let's run the code and see what we get. 

# Running the code

Let’s learn how the statistics of the tests could be improved using the optional weight call back. 

Adjusting the Model: Better Statistics

Let’s learn how the statistics of the tests could be improved using the optional weight call back.

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

Adjusting the Model: Better Statistics

Adding the call back