def executesAllTasksInASingleBuildAndEachTaskAtMostOnce() {
        buildFile << """
            gradle.taskGraph.whenReady { assert !project.hasProperty('graphReady'); ext.graphReady = true }
            task a {
                doLast { task ->
                    project.ext.executedA = task
                }
            }
            task b {
                doLast {