Update boost tree argument checking tests

Author: DavisVaughan

tests/testthat/test_boost_tree.R

@@ -121,8 +121,14 @@ test_that('updating', {
 
 test_that('bad input', {
   expect_error(boost_tree(mode = "bogus"))
-  expect_error(boost_tree(trees = -1))
-  expect_error(boost_tree(min_n = -10))
+  expect_error({
+    bt <- boost_tree(trees = -1)
+    fit(bt, Species ~ ., iris, "xgboost")
+  })
+  expect_error({
+    bt <- boost_tree(min_n = -10)
+    fit(bt, Species ~ ., iris, "xgboost")
+  })
   expect_error(translate(boost_tree(), engine = "wat?"))
   expect_warning(translate(boost_tree(), engine = NULL))
   expect_error(translate(boost_tree(formula = y ~ x)))