What is phpunit.xsd for?

If you open up your phpunit.xml in any project, your main focus is likely on setting up your test suite definitions or overriding environment variables.

But up toward the top of the file, is this line you've probably never paid much attention to:

xsi:noNamespaceSchemaLocation="./vendor/phpunit/phpunit/phpunit.xsd"

What does that mean and how does it help us when working in this configuration file?

The extension .xsd stands for XML Schema Definition. It provides a complete definition of how an XML document can be structured. In our case, that document is the phpunit.xml configuration file.

Just like our database has a schema defining tables, columns, and indexes, our XML document has a defined schema as well.

So this line is telling our editor the "schema location" (see that in the attribute name?) for the XML document we're working on.

As a side note, the "no namespace" part of that attribute name just means that everything it defines is in the default namespace. So instead of having to use a namespace prefix for everything, like <phpunit:testsuites>, we can just use elements and attributes directly, like <testsuites>.

Ok, so how does this schema definition actually help us?

Well, we could open it and read it as a set of local documentation, to see what elements and attributes are allowed. Go ahead, try it! That certainly has some value.

But the real benefit comes when we open up our phpunit.xml file in an editor that supports XML and knows how to use that schema definition. When we do that, it will use the phpunit.xsd file to provide us with code completion and validation as we're editing our PHPUnit configuration.

Here to help,

Joel

P.S. Imagine having a whole book of helpful tips like this one?