Fix spelling in documents (#6948)

* Update roxygen2 doc.

Co-authored-by: fis <jm.yuan@outlook.com>

R-package/tests/testthat/test_basic.R

@@ -331,7 +331,7 @@ test_that("train and predict with non-strict classes", {
   expect_error(pr <- predict(bst, train_dense), regexp = NA)
   expect_equal(pr0, pr)
 
-  # when someone inhertis from xgb.Booster, it should still be possible to use it as xgb.Booster
+  # when someone inherits from xgb.Booster, it should still be possible to use it as xgb.Booster
   class(bst) <- c('super.Booster', 'xgb.Booster')
   expect_error(pr <- predict(bst, train_dense), regexp = NA)
   expect_equal(pr0, pr)
@@ -346,7 +346,7 @@ test_that("max_delta_step works", {
   bst1 <- xgb.train(param, dtrain, nrounds, watchlist, verbose = 1)
   # model with restricted max_delta_step
   bst2 <- xgb.train(param, dtrain, nrounds, watchlist, verbose = 1, max_delta_step = 1)
-  # the no-restriction model is expected to have consistently lower loss during the initial interations
+  # the no-restriction model is expected to have consistently lower loss during the initial iterations
   expect_true(all(bst1$evaluation_log$train_logloss < bst2$evaluation_log$train_logloss))
   expect_lt(mean(bst1$evaluation_log$train_logloss) / mean(bst2$evaluation_log$train_logloss), 0.8)
 })

R-package/tests/testthat/test_monotone.R

@@ -19,5 +19,5 @@ test_that("monotone constraints for regression", {
     pred.ord <- pred[ind]
     expect_true({
         !any(diff(pred.ord) > 0)
-    }, "Monotone Contraint Satisfied")
+    }, "Monotone constraint satisfied")
 })

R-package/tests/testthat/test_poisson_regression.R

@@ -1,9 +1,9 @@
-context('Test poisson regression model')
+context('Test Poisson regression model')
 
 require(xgboost)
 set.seed(1994)
 
-test_that("poisson regression works", {
+test_that("Poisson regression works", {
   data(mtcars)
   bst <- xgboost(data = as.matrix(mtcars[, -11]), label = mtcars[, 11],
                 objective = 'count:poisson', nrounds = 10, verbose = 0)