Refactor rabit tests (#6096)

* Merge rabit tests into XGBoost.
* Run them On CI.
* Simplification for CMake scripts.

tests/cpp/rabit/allreduce_base_test.cc

@@ -0,0 +1,68 @@
+#define RABIT_CXXTESTDEFS_H
+#if !defined(_WIN32)
+#include <gtest/gtest.h>
+
+#include <string>
+#include <iostream>
+#include "../../../rabit/src/allreduce_base.h"
+
+TEST(AllreduceBase, InitTask)
+{
+  rabit::engine::AllreduceBase base;
+
+  std::string rabit_task_id = "rabit_task_id=1";
+  char cmd[rabit_task_id.size()+1];
+  std::copy(rabit_task_id.begin(), rabit_task_id.end(), cmd);
+  cmd[rabit_task_id.size()] = '\0';
+
+  char* argv[] = {cmd};
+  base.Init(1, argv);
+  EXPECT_EQ(base.task_id, "1");
+}
+
+TEST(AllreduceBase, InitWithCacheOn)
+{
+  rabit::engine::AllreduceBase base;
+
+  std::string rabit_task_id = "rabit_task_id=1";
+  char cmd[rabit_task_id.size()+1];
+  std::copy(rabit_task_id.begin(), rabit_task_id.end(), cmd);
+  cmd[rabit_task_id.size()] = '\0';
+
+  std::string rabit_bootstrap_cache = "rabit_bootstrap_cache=1";
+  char cmd2[rabit_bootstrap_cache.size()+1];
+  std::copy(rabit_bootstrap_cache.begin(), rabit_bootstrap_cache.end(), cmd2);
+  cmd2[rabit_bootstrap_cache.size()] = '\0';
+
+  std::string rabit_debug = "rabit_debug=1";
+  char cmd3[rabit_debug.size()+1];
+  std::copy(rabit_debug.begin(), rabit_debug.end(), cmd3);
+  cmd3[rabit_debug.size()] = '\0';
+
+  char* argv[] = {cmd, cmd2, cmd3};
+  base.Init(3, argv);
+  EXPECT_EQ(base.task_id, "1");
+  EXPECT_TRUE(base.rabit_bootstrap_cache);
+  EXPECT_EQ(base.rabit_debug, 1);
+}
+
+TEST(AllreduceBase, InitWithRingReduce)
+{
+  rabit::engine::AllreduceBase base;
+
+  std::string rabit_task_id = "rabit_task_id=1";
+  char cmd[rabit_task_id.size()+1];
+  std::copy(rabit_task_id.begin(), rabit_task_id.end(), cmd);
+  cmd[rabit_task_id.size()] = '\0';
+
+  std::string rabit_reduce_ring_mincount = "rabit_reduce_ring_mincount=1";
+  char cmd2[rabit_reduce_ring_mincount.size()+1];
+  std::copy(rabit_reduce_ring_mincount.begin(), rabit_reduce_ring_mincount.end(), cmd2);
+  cmd2[rabit_reduce_ring_mincount.size()] = '\0';
+
+  char* argv[] = {cmd, cmd2};
+  base.Init(2, argv);
+  EXPECT_EQ(base.task_id, "1");
+  EXPECT_EQ(base.reduce_ring_mincount, 1ul);
+}
+#endif  // !defined(_WIN32)