def METHOD_NAME(self):
    for i in range(3):
        self.op.setConstant(i)
        aimg = self.renderScene(self.scene, "/tmp/a_%03d.png" % i)
        assert numpy.all(aimg[:, :, 0] == i), "!= %d, [0,0,0]=%d" % (i, aimg[0, 0, 0])
        self.op.setConstant(42)
        self.op.setDelay(1)
        aimg = self.renderScene(self.scene, joinRendering=False, exportFilename="/tmp/x_%03d.png" % i)
        # this should be "i", not 255 (the default background for the imagescene)
        assert numpy.all(aimg[:, :, 0] == i), "!= %d, [0,0,0]=%d" % (i, aimg[0, 0, 0])
        # Now give the scene time to update before we change it again...
        self.scene.joinRenderingAllTiles(viewport_only=False)