diff --git a/R-package/tests/testthat/test_basic.R b/R-package/tests/testthat/test_basic.R
index 4420c9105..e052499dd 100644
--- a/R-package/tests/testthat/test_basic.R
+++ b/R-package/tests/testthat/test_basic.R
@@ -1,6 +1,3 @@
-require(xgboost)
-library(Matrix)
-
 context("basic functions")
 
 data(agaricus.train, package = 'xgboost')
diff --git a/R-package/tests/testthat/test_callbacks.R b/R-package/tests/testthat/test_callbacks.R
index 69894bd05..6540ef0b3 100644
--- a/R-package/tests/testthat/test_callbacks.R
+++ b/R-package/tests/testthat/test_callbacks.R
@@ -1,9 +1,4 @@
 # More specific testing of callbacks
-
-require(xgboost)
-require(data.table)
-require(titanic)
-
 context("callbacks")
 
 data(agaricus.train, package = 'xgboost')
@@ -84,7 +79,7 @@ test_that("cb.evaluation.log works as expected", {
                list(c(iter = 1, bst_evaluation), c(iter = 2, bst_evaluation)))
   expect_silent(f(finalize = TRUE))
   expect_equal(evaluation_log,
-               data.table(iter = 1:2, train_auc = c(0.9, 0.9), test_auc = c(0.8, 0.8)))
+               data.table::data.table(iter = 1:2, train_auc = c(0.9, 0.9), test_auc = c(0.8, 0.8)))
 
   bst_evaluation_err  <- c('train-auc' = 0.1, 'test-auc' = 0.2)
   evaluation_log <- list()
@@ -101,7 +96,7 @@ test_that("cb.evaluation.log works as expected", {
                     c(iter = 2, c(bst_evaluation, bst_evaluation_err))))
   expect_silent(f(finalize = TRUE))
   expect_equal(evaluation_log,
-               data.table(iter = 1:2,
+               data.table::data.table(iter = 1:2,
                           train_auc_mean = c(0.9, 0.9), train_auc_std = c(0.1, 0.1),
                           test_auc_mean = c(0.8, 0.8), test_auc_std = c(0.2, 0.2)))
 })
@@ -256,6 +251,9 @@ test_that("early stopping using a specific metric works", {
 })
 
 test_that("early stopping works with titanic", {
+  if (!requireNamespace("titanic")) {
+    testthat::skip("Optional testing dependency 'titanic' not found.")
+  }
   # This test was inspired by https://github.com/dmlc/xgboost/issues/5935
   # It catches possible issues on noLD R
   titanic <- titanic::titanic_train
diff --git a/R-package/tests/testthat/test_custom_objective.R b/R-package/tests/testthat/test_custom_objective.R
index d98e7045a..95be4140f 100644
--- a/R-package/tests/testthat/test_custom_objective.R
+++ b/R-package/tests/testthat/test_custom_objective.R
@@ -1,7 +1,5 @@
 context('Test models with custom objective')
 
-require(xgboost)
-
 set.seed(1994)
 
 data(agaricus.train, package = 'xgboost')
diff --git a/R-package/tests/testthat/test_dmatrix.R b/R-package/tests/testthat/test_dmatrix.R
index 74d172f69..3c922e9a0 100644
--- a/R-package/tests/testthat/test_dmatrix.R
+++ b/R-package/tests/testthat/test_dmatrix.R
@@ -1,6 +1,3 @@
-require(xgboost)
-require(Matrix)
-
 context("testing xgb.DMatrix functionality")
 
 data(agaricus.test, package = 'xgboost')
@@ -123,7 +120,7 @@ test_that("xgb.DMatrix: colnames", {
 test_that("xgb.DMatrix: nrow is correct for a very sparse matrix", {
   set.seed(123)
   nr <- 1000
-  x <- rsparsematrix(nr, 100, density = 0.0005)
+  x <- Matrix::rsparsematrix(nr, 100, density = 0.0005)
   # we want it very sparse, so that last rows are empty
   expect_lt(max(x@i), nr)
   dtest <- xgb.DMatrix(x)
diff --git a/R-package/tests/testthat/test_feature_weights.R b/R-package/tests/testthat/test_feature_weights.R
index 580f58456..bb3802979 100644
--- a/R-package/tests/testthat/test_feature_weights.R
+++ b/R-package/tests/testthat/test_feature_weights.R
@@ -1,5 +1,3 @@
-library(xgboost)
-
 context("feature weights")
 
 test_that("training with feature weights works", {
diff --git a/R-package/tests/testthat/test_gc_safety.R b/R-package/tests/testthat/test_gc_safety.R
index fb80757c5..f77af1eab 100644
--- a/R-package/tests/testthat/test_gc_safety.R
+++ b/R-package/tests/testthat/test_gc_safety.R
@@ -1,5 +1,3 @@
-require(xgboost)
-
 context("Garbage Collection Safety Check")
 
 test_that("train and prediction when gctorture is on", {
diff --git a/R-package/tests/testthat/test_glm.R b/R-package/tests/testthat/test_glm.R
index 270267a0f..2d050945a 100644
--- a/R-package/tests/testthat/test_glm.R
+++ b/R-package/tests/testthat/test_glm.R
@@ -1,7 +1,5 @@
 context('Test generalized linear models')
 
-require(xgboost)
-
 test_that("gblinear works", {
   data(agaricus.train, package = 'xgboost')
   data(agaricus.test, package = 'xgboost')
diff --git a/R-package/tests/testthat/test_helpers.R b/R-package/tests/testthat/test_helpers.R
index 2eab5624f..01436f48a 100644
--- a/R-package/tests/testthat/test_helpers.R
+++ b/R-package/tests/testthat/test_helpers.R
@@ -1,10 +1,11 @@
-library(testthat)
 context('Test helper functions')
 
-require(xgboost)
-require(data.table)
-require(Matrix)
-require(vcd, quietly = TRUE)
+VCD_AVAILABLE <- requireNamespace("vcd", quietly = TRUE)
+.skip_if_vcd_not_available <- function() {
+    if (!VCD_AVAILABLE) {
+        testthat::skip("Optional testing dependency 'vcd' not found.")
+    }
+}
 
 float_tolerance <- 5e-6
 
@@ -12,25 +13,28 @@ float_tolerance <- 5e-6
 flag_32bit <- .Machine$sizeof.pointer != 8
 
 set.seed(1982)
-data(Arthritis)
-df <- data.table(Arthritis, keep.rownames = FALSE)
-df[, AgeDiscret := as.factor(round(Age / 10, 0))]
-df[, AgeCat := as.factor(ifelse(Age > 30, "Old", "Young"))]
-df[, ID := NULL]
-sparse_matrix <- sparse.model.matrix(Improved~.-1, data = df) # nolint
-label <- df[, ifelse(Improved == "Marked", 1, 0)]
 
-# binary
 nrounds <- 12
-bst.Tree <- xgboost(data = sparse_matrix, label = label, max_depth = 9,
-                    eta = 1, nthread = 2, nrounds = nrounds, verbose = 0,
-                    objective = "binary:logistic", booster = "gbtree")
+if (isTRUE(VCD_AVAILABLE)) {
+    data(Arthritis, package = "vcd")
+    df <- data.table::data.table(Arthritis, keep.rownames = FALSE)
+    df[, AgeDiscret := as.factor(round(Age / 10, 0))]
+    df[, AgeCat := as.factor(ifelse(Age > 30, "Old", "Young"))]
+    df[, ID := NULL]
+    sparse_matrix <- Matrix::sparse.model.matrix(Improved~.-1, data = df) # nolint
+    label <- df[, ifelse(Improved == "Marked", 1, 0)]
 
-bst.GLM <- xgboost(data = sparse_matrix, label = label,
-                   eta = 1, nthread = 1, nrounds = nrounds, verbose = 0,
-                   objective = "binary:logistic", booster = "gblinear")
+    # binary
+    bst.Tree <- xgboost(data = sparse_matrix, label = label, max_depth = 9,
+                        eta = 1, nthread = 2, nrounds = nrounds, verbose = 0,
+                        objective = "binary:logistic", booster = "gbtree")
 
-feature.names <- colnames(sparse_matrix)
+    bst.GLM <- xgboost(data = sparse_matrix, label = label,
+                       eta = 1, nthread = 1, nrounds = nrounds, verbose = 0,
+                       objective = "binary:logistic", booster = "gblinear")
+
+    feature.names <- colnames(sparse_matrix)
+}
 
 # multiclass
 mlabel <- as.numeric(iris$Species) - 1
@@ -45,6 +49,7 @@ mbst.GLM <- xgboost(data = as.matrix(iris[, -5]), label = mlabel, verbose = 0,
 
 
 test_that("xgb.dump works", {
+  .skip_if_vcd_not_available()
   if (!flag_32bit)
     expect_length(xgb.dump(bst.Tree), 200)
   dump_file <- file.path(tempdir(), 'xgb.model.dump')
@@ -60,6 +65,7 @@ test_that("xgb.dump works", {
 })
 
 test_that("xgb.dump works for gblinear", {
+  .skip_if_vcd_not_available()
   expect_length(xgb.dump(bst.GLM), 14)
   # also make sure that it works properly for a sparse model where some coefficients
   # are 0 from setting large L1 regularization:
@@ -76,6 +82,7 @@ test_that("xgb.dump works for gblinear", {
 })
 
 test_that("predict leafs works", {
+  .skip_if_vcd_not_available()
   # no error for gbtree
   expect_error(pred_leaf <- predict(bst.Tree, sparse_matrix, predleaf = TRUE), regexp = NA)
   expect_equal(dim(pred_leaf), c(nrow(sparse_matrix), nrounds))
@@ -84,6 +91,7 @@ test_that("predict leafs works", {
 })
 
 test_that("predict feature contributions works", {
+  .skip_if_vcd_not_available()
   # gbtree binary classifier
   expect_error(pred_contr <- predict(bst.Tree, sparse_matrix, predcontrib = TRUE), regexp = NA)
   expect_equal(dim(pred_contr), c(nrow(sparse_matrix), ncol(sparse_matrix) + 1))
@@ -187,6 +195,7 @@ test_that("SHAPs sum to predictions, with or without DART", {
 })
 
 test_that("xgb-attribute functionality", {
+  .skip_if_vcd_not_available()
   val <- "my attribute value"
   list.val <- list(my_attr = val, a = 123, b = 'ok')
   list.ch <- list.val[order(names(list.val))]
@@ -224,6 +233,7 @@ if (grepl('Windows', Sys.info()[['sysname']]) ||
     grepl('Linux', Sys.info()[['sysname']]) ||
     grepl('Darwin', Sys.info()[['sysname']])) {
     test_that("xgb-attribute numeric precision", {
+      .skip_if_vcd_not_available()
       # check that lossless conversion works with 17 digits
       # numeric -> character -> numeric
       X <- 10^runif(100, -20, 20)
@@ -242,6 +252,7 @@ if (grepl('Windows', Sys.info()[['sysname']]) ||
 }
 
 test_that("xgb.Booster serializing as R object works", {
+  .skip_if_vcd_not_available()
   saveRDS(bst.Tree, 'xgb.model.rds')
   bst <- readRDS('xgb.model.rds')
   dtrain <- xgb.DMatrix(sparse_matrix, label = label)
@@ -260,6 +271,7 @@ test_that("xgb.Booster serializing as R object works", {
 })
 
 test_that("xgb.model.dt.tree works with and without feature names", {
+  .skip_if_vcd_not_available()
   names.dt.trees <- c("Tree", "Node", "ID", "Feature", "Split", "Yes", "No", "Missing", "Quality", "Cover")
   dt.tree <- xgb.model.dt.tree(feature_names = feature.names, model = bst.Tree)
   expect_equal(names.dt.trees, names(dt.tree))
@@ -279,16 +291,18 @@ test_that("xgb.model.dt.tree works with and without feature names", {
 
   # using integer node ID instead of character
   dt.tree.int <- xgb.model.dt.tree(model = bst.Tree, use_int_id = TRUE)
-  expect_equal(as.integer(tstrsplit(dt.tree$Yes, '-')[[2]]), dt.tree.int$Yes)
-  expect_equal(as.integer(tstrsplit(dt.tree$No, '-')[[2]]), dt.tree.int$No)
-  expect_equal(as.integer(tstrsplit(dt.tree$Missing, '-')[[2]]), dt.tree.int$Missing)
+  expect_equal(as.integer(data.table::tstrsplit(dt.tree$Yes, '-')[[2]]), dt.tree.int$Yes)
+  expect_equal(as.integer(data.table::tstrsplit(dt.tree$No, '-')[[2]]), dt.tree.int$No)
+  expect_equal(as.integer(data.table::tstrsplit(dt.tree$Missing, '-')[[2]]), dt.tree.int$Missing)
 })
 
 test_that("xgb.model.dt.tree throws error for gblinear", {
+  .skip_if_vcd_not_available()
   expect_error(xgb.model.dt.tree(model = bst.GLM))
 })
 
 test_that("xgb.importance works with and without feature names", {
+  .skip_if_vcd_not_available()
   importance.Tree <- xgb.importance(feature_names = feature.names, model = bst.Tree)
   if (!flag_32bit)
     expect_equal(dim(importance.Tree), c(7, 4))
@@ -354,6 +368,7 @@ test_that("xgb.importance works with and without feature names", {
 })
 
 test_that("xgb.importance works with GLM model", {
+  .skip_if_vcd_not_available()
   importance.GLM <- xgb.importance(feature_names = feature.names, model = bst.GLM)
   expect_equal(dim(importance.GLM), c(10, 2))
   expect_equal(colnames(importance.GLM), c("Feature", "Weight"))
@@ -369,6 +384,7 @@ test_that("xgb.importance works with GLM model", {
 })
 
 test_that("xgb.model.dt.tree and xgb.importance work with a single split model", {
+  .skip_if_vcd_not_available()
   bst1 <- xgboost(data = sparse_matrix, label = label, max_depth = 1,
                   eta = 1, nthread = 2, nrounds = 1, verbose = 0,
                   objective = "binary:logistic")
@@ -380,16 +396,19 @@ test_that("xgb.model.dt.tree and xgb.importance work with a single split model",
 })
 
 test_that("xgb.plot.tree works with and without feature names", {
+  .skip_if_vcd_not_available()
   expect_silent(xgb.plot.tree(feature_names = feature.names, model = bst.Tree))
   expect_silent(xgb.plot.tree(model = bst.Tree))
 })
 
 test_that("xgb.plot.multi.trees works with and without feature names", {
+  .skip_if_vcd_not_available()
   xgb.plot.multi.trees(model = bst.Tree, feature_names = feature.names, features_keep = 3)
   xgb.plot.multi.trees(model = bst.Tree, features_keep = 3)
 })
 
 test_that("xgb.plot.deepness works", {
+  .skip_if_vcd_not_available()
   d2p <- xgb.plot.deepness(model = bst.Tree)
   expect_equal(colnames(d2p), c("ID", "Tree", "Depth", "Cover", "Weight"))
   xgb.plot.deepness(model = bst.Tree, which = "med.depth")
@@ -397,6 +416,7 @@ test_that("xgb.plot.deepness works", {
 })
 
 test_that("xgb.shap.data works when top_n is provided", {
+  .skip_if_vcd_not_available()
   data_list <- xgb.shap.data(data = sparse_matrix, model = bst.Tree, top_n = 2)
   expect_equal(names(data_list), c("data", "shap_contrib"))
   expect_equal(NCOL(data_list$data), 2)
@@ -414,12 +434,14 @@ test_that("xgb.shap.data works when top_n is provided", {
 })
 
 test_that("xgb.shap.data works with subsampling", {
+  .skip_if_vcd_not_available()
   data_list <- xgb.shap.data(data = sparse_matrix, model = bst.Tree, top_n = 2, subsample = 0.8)
   expect_equal(NROW(data_list$data), as.integer(0.8 * nrow(sparse_matrix)))
   expect_equal(NROW(data_list$data), NROW(data_list$shap_contrib))
 })
 
 test_that("prepare.ggplot.shap.data works", {
+  .skip_if_vcd_not_available()
   data_list <- xgb.shap.data(data = sparse_matrix, model = bst.Tree, top_n = 2)
   plot_data <- prepare.ggplot.shap.data(data_list, normalize = TRUE)
   expect_s3_class(plot_data, "data.frame")
@@ -430,11 +452,13 @@ test_that("prepare.ggplot.shap.data works", {
 })
 
 test_that("xgb.plot.shap works", {
+  .skip_if_vcd_not_available()
   sh <- xgb.plot.shap(data = sparse_matrix, model = bst.Tree, top_n = 2, col = 4)
   expect_equal(names(sh), c("data", "shap_contrib"))
 })
 
 test_that("xgb.plot.shap.summary works", {
+  .skip_if_vcd_not_available()
   expect_silent(xgb.plot.shap.summary(data = sparse_matrix, model = bst.Tree, top_n = 2))
   expect_silent(xgb.ggplot.shap.summary(data = sparse_matrix, model = bst.Tree, top_n = 2))
 })
diff --git a/R-package/tests/testthat/test_interactions.R b/R-package/tests/testthat/test_interactions.R
index e90467cdc..a658fc81f 100644
--- a/R-package/tests/testthat/test_interactions.R
+++ b/R-package/tests/testthat/test_interactions.R
@@ -1,7 +1,5 @@
 context('Test prediction of feature interactions')
 
-require(xgboost)
-
 set.seed(123)
 
 test_that("predict feature interactions works", {
diff --git a/R-package/tests/testthat/test_io.R b/R-package/tests/testthat/test_io.R
index 5b2bc4265..c2cb1a1a8 100644
--- a/R-package/tests/testthat/test_io.R
+++ b/R-package/tests/testthat/test_io.R
@@ -1,7 +1,4 @@
 context("Test model IO.")
-## some other tests are in test_basic.R
-require(xgboost)
-require(testthat)
 
 data(agaricus.train, package = "xgboost")
 data(agaricus.test, package = "xgboost")
diff --git a/R-package/tests/testthat/test_model_compatibility.R b/R-package/tests/testthat/test_model_compatibility.R
index 6a35ca4b3..cb8c432fa 100644
--- a/R-package/tests/testthat/test_model_compatibility.R
+++ b/R-package/tests/testthat/test_model_compatibility.R
@@ -1,6 +1,3 @@
-require(xgboost)
-require(jsonlite)
-
 context("Models from previous versions of XGBoost can be loaded")
 
 metadata <- list(
diff --git a/R-package/tests/testthat/test_monotone.R b/R-package/tests/testthat/test_monotone.R
index 756863061..cb5827698 100644
--- a/R-package/tests/testthat/test_monotone.R
+++ b/R-package/tests/testthat/test_monotone.R
@@ -1,5 +1,3 @@
-require(xgboost)
-
 context("monotone constraints")
 
 set.seed(1024)
diff --git a/R-package/tests/testthat/test_parameter_exposure.R b/R-package/tests/testthat/test_parameter_exposure.R
index 86413174b..47524fbfc 100644
--- a/R-package/tests/testthat/test_parameter_exposure.R
+++ b/R-package/tests/testthat/test_parameter_exposure.R
@@ -1,7 +1,5 @@
 context('Test model params and call are exposed to R')
 
-require(xgboost)
-
 data(agaricus.train, package = 'xgboost')
 data(agaricus.test, package = 'xgboost')
 
diff --git a/R-package/tests/testthat/test_poisson_regression.R b/R-package/tests/testthat/test_poisson_regression.R
index 4f3527cdb..b17c6c072 100644
--- a/R-package/tests/testthat/test_poisson_regression.R
+++ b/R-package/tests/testthat/test_poisson_regression.R
@@ -1,6 +1,5 @@
 context('Test Poisson regression model')
 
-require(xgboost)
 set.seed(1994)
 
 test_that("Poisson regression works", {
diff --git a/R-package/tests/testthat/test_ranking.R b/R-package/tests/testthat/test_ranking.R
index 7a352bea2..9e8d0156e 100644
--- a/R-package/tests/testthat/test_ranking.R
+++ b/R-package/tests/testthat/test_ranking.R
@@ -1,12 +1,12 @@
-require(xgboost)
-require(Matrix)
-
 context('Learning to rank')
 
 test_that('Test ranking with unweighted data', {
-  X <- sparseMatrix(i = c(2, 3, 7, 9, 12, 15, 17, 18),
-                    j = c(1, 1, 2, 2,  3,  3,  4,  4),
-                    x = rep(1.0, 8), dims = c(20, 4))
+  X <- Matrix::sparseMatrix(
+    i = c(2, 3, 7, 9, 12, 15, 17, 18)
+    , j = c(1, 1, 2, 2,  3,  3,  4,  4)
+    , x = rep(1.0, 8)
+    , dims = c(20, 4)
+  )
   y <- c(0, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0)
   group <- c(5, 5, 5, 5)
   dtrain <- xgb.DMatrix(X, label = y, group = group)
@@ -20,9 +20,12 @@ test_that('Test ranking with unweighted data', {
 })
 
 test_that('Test ranking with weighted data', {
-  X <- sparseMatrix(i = c(2, 3, 7, 9, 12, 15, 17, 18),
-                    j = c(1, 1, 2, 2,  3,  3,  4,  4),
-                    x = rep(1.0, 8), dims = c(20, 4))
+  X <- Matrix::sparseMatrix(
+    i = c(2, 3, 7, 9, 12, 15, 17, 18)
+    , j = c(1, 1, 2, 2,  3,  3,  4,  4)
+    , x = rep(1.0, 8)
+    , dims = c(20, 4)
+  )
   y <- c(0, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0)
   group <- c(5, 5, 5, 5)
   weight <- c(1.0, 2.0, 3.0, 4.0)
diff --git a/R-package/tests/testthat/test_update.R b/R-package/tests/testthat/test_update.R
index 541fdf68e..887ffeb06 100644
--- a/R-package/tests/testthat/test_update.R
+++ b/R-package/tests/testthat/test_update.R
@@ -1,5 +1,3 @@
-require(xgboost)
-
 context("update trees in an existing model")
 
 data(agaricus.train, package = 'xgboost')