Gradle aggregate task outputs

Question

How do I pass a task's outputs forward as the outputs of a subsequent task?

I want to dynamically register subtasks in a loop and aggregate them. For example, I want the "assemble" task to include both .tar archives created by "assemble_test" and "assemble_prod".

This works but definitely feels wrong. What am I missing?

plugins {
    id "base"
}

["test", "prod"].each { env ->
    def task = tasks.register("assemble_${env}", Tar) {
        archiveFileName = "output-${env}.tar"
        from env
    }
    assemble.outputs.files(task.get().outputs.files)
}