Property changed signal not sent

import QtQuick 2.15

Item {
    id: root
    width: 240
    height: 220
 
    PropTest {
        id: propertyTest
        onOutputChanged: console.log("output", output)
    }

    Keys.onPressed: {
        console.log("Key", event.key)
        if (event.key === Qt.Key_S) {
            //console.log("Set input. Output was", propertyTest.output)
            propertyTest.input = propertyTest.input + 1
        }
    }
}

import QtQuick 2.15
Item {
    readonly property int output: input
    property int input: 0
}