There are different ways in which we can run our PHPUnit tests. We can either run a full unit test, a test suite or one specific test as shown in following commands:

To run all the tests available from the custom modules directory:

Simple way to do this is to add form alter in a custom module like this

One of the reasons we are using services instead of plain classes is possibility to swap out class that each service uses.  So what we need to do is we need to create a new class that's overriding an existing service class, and then we need to alter the service container to use our new class.

Jquery is still standard part of drupal core and when using JavaScript or Ajax you will probably use Jquery and Jquery once function. Code can be found in core/assets/vendor/jquery-once/jquery.once.js  so you could look how it works. It is pretty similar as in D7, look at the comments on how to use it.

In drupal 8 plugins are everywhere, so to get most out of them you will sometimes want to alter them. If you look at definitions of each plugin manager, you will see that all of them have something specific in their constructors, it is the line below

You are using get with fieldname and you are getting array as result, to get value as string, use getString() method like below

$entity->get("fieldName")->getString()

Lets first talk about what does hook_views_data_alter() do in first place. Views is a query editor, it queries DB, so this hook alters how our data is queried. As in views UI you add, fields, filters, sorts, relationships, here you will have an exposure of all DB tables you can make queries on and data on what to use for fields, filters and sorting.

This one is one of the bigger surprises in drupal 8. Form building is straight forward, basic OOP bases on symfony, but then you want your forms to be translatable, you are in for a ride. First you will need to have schema yaml files in install and schema directory.

Currency symbol is not stored in order, so to get it, you need to dig a bit deeper and fetch currency object.
I am assuming you have order stored in $this->order so then we get currency code and with that we load commerce_currency through entity type manager and use getSymbol method to get the symbol.

If you wan to get coupon entity from order there is a quick magic method to do that. First load order by some property, we can use ID