test_that("Only strings are accepted for UniProt IDs", {
   expect_null(accessUniprot(NULL))
   expect_null(accessUniprot(4))
   expect_null(accessUniprot(3.14))
 })
 
 test_that("Warning is raised if UniProt ID is incorrect", {
   expect_null(accessUniprot("Hello"))
   expect_null(accessUniprot("A00000"))
 })