class(plot) (`actual`) not equal to c("gg", "ggplot") (`expected`).

`actual`:        "ggplot2::ggplot" "ggplot" "ggplot2::gg" "S7_object" "gg"    
`expected[2:2]`:                                                      "ggplot"

test_that("plot_QC_Tree generates the correct plot", {

"plot_QC_Tree generates the correct plot"