app.rs

Let's start with the same struct as we had before:

{{#include @code/tutorials/ratatui-counter-app/src/app.rs:application}}

We can add additional methods to this Application struct:

{{#include @code/tutorials/ratatui-counter-app/src/app.rs:application_impl}}

We use the principle of encapsulation to expose an interface to modify the state. In this particular instance, it may seem like overkill but it is good practice nonetheless.

The practical advantage of this is that it makes the state changes easy to test.

{{#include @code/tutorials/ratatui-counter-app/src/app.rs:application_test}}

:::tip

You can test a single function by writing out fully qualified module path to the test function, like so:

cargo test -- app::tests::test_app_increment_counter --nocapture

Or even test all functions that start with test_app_ by doing this:

cargo test -- app::tests::test_app_ --nocapture

The --nocapture flag prints stdout and stderr to the console, which can help debugging tests.

:::