public function testStart()
{
$fn = function () {
};
$this->supA->shouldReceive('start')->once()->with($fn);
$this->supB->shouldReceive('start')->once()->with($fn);
$this->supC->shouldReceive('start')->once()->with($fn);
$this->assertSame($this->sup, $this->sup->start($fn));
$this->assertNull($this->sup->stderr);
$this->assertNull($this->sup->stdout);
}