Fix gpu_hist apply_split test. (#4158)

include/xgboost/tree_model.h

@@ -328,7 +328,7 @@ class RegTree {
     nodes_[node.LeftChild()].SetParent(nid, true);
     nodes_[node.RightChild()].SetParent(nid, false);
     node.SetSplit(split_index, split_value,
-                         default_left);
+                  default_left);
     // mark right child as 0, to indicate fresh leaf
     nodes_[pleft].SetLeaf(left_leaf_weight, 0);
     nodes_[pright].SetLeaf(right_leaf_weight, 0);

tests/cpp/predictor/test_gpu_predictor.cu

@@ -90,6 +90,7 @@ TEST(gpu_predictor, Test) {
   delete dmat;
 }
 
+#if defined(XGBOOST_USE_NCCL)
 // Test whether pickling preserves predictor parameters
 TEST(gpu_predictor, MGPU_PicklingTest) {
   int ngpu;
@@ -163,7 +164,9 @@ TEST(gpu_predictor, MGPU_PicklingTest) {
 
   CheckCAPICall(XGBoosterFree(bst2));
 }
+#endif  // defined(XGBOOST_USE_NCCL)
 
+#if defined(XGBOOST_USE_NCCL)
 // multi-GPU predictor test
 TEST(gpu_predictor, MGPU_Test) {
   std::unique_ptr<Predictor> gpu_predictor =
@@ -202,6 +205,6 @@ TEST(gpu_predictor, MGPU_Test) {
     delete dmat;
   }
 }
-
+#endif  // defined(XGBOOST_USE_NCCL)
 }  // namespace predictor
 }  // namespace xgboost

tests/cpp/tree/test_gpu_hist.cu

@@ -5,6 +5,9 @@
 #include <thrust/device_vector.h>
 #include <xgboost/base.h>
 #include <random>
+#include <string>
+#include <vector>
+
 #include "../helpers.h"
 #include "gtest/gtest.h"
 
@@ -315,6 +318,8 @@ TEST(GpuHist, ApplySplit) {
   int constexpr n_cols = 8;
 
   TrainParam param;
+  std::vector<std::pair<std::string, std::string>> args = {};
+  param.InitAllowUnknown(args);
 
   // Initialize shard
   for (size_t i = 0; i < n_cols; ++i) {