How do I determine which tests were skipped in testthat?

Question

When I run unit test locally for caretEnsemble, I get some tests skips. 3 of them are expected, 2 of them are not:

Rscript -e "Sys.setenv(NOT_CRAN='true'); devtools::test(stop_on_failure=TRUE, stop_on_warning=TRUE)"
ℹ Testing caretEnsemble
✔ | F W  S  OK | Context
✔ |      3   0 | Test skips are working correctly                                                                                                                                                                                                                                                                                                                           
✔ |        279 | Ancillary caretList functions and errors [1.8s]                                                                                                                                                                                                                                                                                                            
⠏ |          0 | We can fit models with a mix of methodList and tuneList                                                                                                                                                                                                                                                                                                    ✔ |          4 | We can fit models with a mix of methodList and tuneList [2.6s]                                                                                                                                                                                                                                                                                             
✔ |         40 | We can handle different CV methods [11.9s]                                                                                                                                                                                                                                                                                                                 
✔ |         31 | Classification models [9.6s]                                                                                                                                                                                                                                                                                                                               
✔ |          4 | User tuneTest parameters are respected and model is ensembled [1.4s]                                                                                                                                                                                                                                                                                       
✔ |          4 | Formula interface for caretList works [2.0s]                                                                                                                                                                                                                                                                                                               
✔ |          4 | Regression models [1.4s]                                                                                                                                                                                                                                                                                                                                   
✔ |      1  10 | Does stacking and prediction work? [2.3s]                                                                                                                                                                                                                                                                                                                  
✔ |         12 | Prediction errors for caretStack work as expected [1.8s]                                                                                                                                                                                                                                                                                                   
✔ |         25 | Do classifier predictions use the correct target classes? [1.9s]                                                                                                                                                                                                                                                                                           
✔ |          1 | Test errors and warnings                                                                                                                                                                                                                                                                                                                                   
✔ |          8 | Test metric and residual extraction [1.4s]                                                                                                                                                                                                                                                                                                                 
✔ |         20 | Does ensembling and prediction work? [1.3s]                                                                                                                                                                                                                                                                                                                
✔ |          3 | Does ensembling work with models with differing predictors                                                                                                                                                                                                                                                                                                 
✔ |         16 | Does ensemble prediction work with new data [1.2s]                                                                                                                                                                                                                                                                                                         
✔ |         15 | Do ensembles of custom models work?                                                                                                                                                                                                                                                                                                                        
✔ |      1  18 | Does variable importance work? [12.2s]                                                                                                                                                                                                                                                                                                                     
✔ |         16 | Do metric extraction functions work as expected [1.1s]                                                                                                                                                                                                                                                                                                     
✔ |         18 | Testing caretEnsemble generics [2.3s]                                                                                                                                                                                                                                                                                                                      
✔ |         13 | Residual extraction [1.2s]                                                                                                                                                                                                                                                                                                                                 
✔ |         22 | Are ensembles construct accurately [3.8s]                                                                                                                                                                                                                                                                                                                  
✔ |         10 | Do the helper functions work for regression objects? [1.4s]                                                                                                                                                                                                                                                                                                
✔ |         12 | Do the helper functions work for classification objects?                                                                                                                                                                                                                                                                                                   
✔ |         22 | Test weighted standard deviations [1.8s]                                                                                                                                                                                                                                                                                                                   
✔ |          3 | Parallelization works [1.2s]                                                                                                                                                                                                                                                                                                                               
✔ |         12 | Ancillary caretList S3 Generic Functions Extensions [3.3s]              

How do I make testthat or devtools tell me WHICH tests it is skipping (and why)?

(edit) follow up question: I used a binary search to find one of the skipped tests, and it is:

test_that("caretStack plots", {
  test_plot_file <- "caretEnsemble_test_plots.png"
  ens.reg <- caretStack(
    models.reg,
    method = "gbm", tuneLength = 2, verbose = FALSE,
    trControl = trainControl(number = 2, allowParallel = FALSE)
  )
  png(filename = test_plot_file)
  plot(ens.reg)
  dotplot(ens.reg, metric = "RMSE")
  dev.off()
  unlink(test_plot_file)
})

There's no skip statement at all there— why would testthat skip this test?

(edit 2): Ok testthat skips tests if there's no "expects" in them. Whats the best way to test that a plot is correctly generated? Capture the file and check that it exists?