Add a test to expect warning for k=2 registration

tests/testthat/test-registration_wrapper.R

@@ -0,0 +1,35 @@
+## Ensure reproducibility of example data
+set.seed(20220907)
+
+## Generate example data
+sce <- scuttle::mockSCE()
+
+## Add some sample IDs
+sce$sample_id <- sample(LETTERS[1:5], ncol(sce), replace = TRUE)
+
+## Add a sample-level covariate: age
+ages <- rnorm(5, mean = 20, sd = 4)
+names(ages) <- LETTERS[1:5]
+sce$age <- ages[sce$sample_id]
+
+## add variable with one group
+sce$batch <- "batch1"
+
+## Add gene-level information
+rowData(sce)$ensembl <- paste0("ENSG", seq_len(nrow(sce)))
+rowData(sce)$gene_name <- paste0("gene", seq_len(nrow(sce)))
+
+
+test_that("warning for k=2 variable",
+          example_modeling_results <- expect_warning(
+            registration_wrapper(
+              sce,
+              var_registration ="Treatment",
+              var_sample_id ="sample_id",
+              covars = c("age"),
+              gene_ensembl = "ensembl",
+              gene_name = "gene_name",
+              suffix = "wrapper"
+            )
+          )
+)