"A non-empty PSR-4 prefix must end with a namespace separator"

I am building an app with the following structure:

├── README.md
├── composer.json
├── index.php
└── src
    └── test.php

... and my composer.json file looks like this:

{
    "minimum-stability" : "alpha",
    "name" : "patrick/changedetection",
    "description" : "A change detection script for observing additions to web pages",
    "license" : "MIT",
    "autoload" : {
        "psr-4" : {
            "patrick\\changedetection\\" : [
                "src/"
            ]
        }
    }
}

But when I run composer install, I get

[InvalidArgumentException] A non-empty PSR-4 prefix must end with a namespace separator.

What do I need to do in order to correctly autoload my test.php file?

from "A non-empty PSR-4 prefix must end with a namespace separator"