Why is my post controller returning a 404?

I’ve created and enabled a module at app/code/Post/Test:

app/code/Post/Test/registration.php:

<?php

MagentoFrameworkComponentComponentRegistrar::register(
    MagentoFrameworkComponentComponentRegistrar::MODULE,
    'Post_Test',
    __DIR__
);

app/code/Post/Test/etc/module.xml:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Post_Test" setup_version="1.0.0" />
</config>

app/code/Post/Test/etc/frontend/routes.xml:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:App/etc/routes.xsd">
    <router id="standard">
        <route id="post_test" frontName="posttest">
            <module name="Post_Test" />
        </route>
    </router>
</config>

app/code/Post/Test/Controller/Test:

<?php

namespace PostTestController;

use MagentoFrameworkControllerResultRaw;
use MagentoFrameworkAppActionHttpPostActionInterface;

class Test implements HttpPostActionInterface
{
    private $raw;

    public function __construct(Raw $raw)
    {
        $this->raw = $raw;
    }

    public function execute()
    {
        return $this->raw->setContents('foo bar baz');
    }
}

Based on this, I think that my controller should be accessible via a POST request to: http://localhost/posttest/test, but it just gives me a 404.

What am I doing wrong?