Namespaces declared by a theme/plugin should start with the theme/plugin prefix. Found: “eustatos\test_plugin”

Question

At first, we need to update phpcs.xml.

Let’s replace "my_prefix" with your plugin name (then, assuming "eustatos"):

    <rule ref="WordPress.NamingConventions.PrefixAllGlobals">
        <properties>
            <property name="prefixes" type="array">
                <element value="eustatos"/>
            </property>
        </properties>
    </rule>

Then, you can use namespace start with eustatos in project PHP file.

ex:

namespace eustatos\test_plugin;

cf.

Customizable sniff properties · WordPress/WordPress-Coding-Standards Wiki

To execute this check one or more prefixes which should be considered valid must be provided via the $prefixes property in your custom ruleset or via the command-line.

If this property is not set, this sniff will not run.
<rule ref="WordPress.NamingConventions.PrefixAllGlobals">
  <properties>
      <property name="prefixes" type="array">
          <element value="my_prefix"/>
          <element value="tgmpa"/>
      </property>

  </properties>
</rule>