composer/tests/Composer/Test/Plugin/Fixtures/plugin-v4/composer.json

{
    "name": "plugin-v4",
    "version": "4.0.0",
    "type": "composer-plugin",
    "autoload": { "psr-0": { "Installer": "" } },
    "extra": {
        "class": [
            "Installer\\Plugin1",
            "Installer\\Plugin2"
        ]
    },
    "require": {
        "composer-plugin-api": "^2.0"
    }
}