Define pair generation strategies for LTR. (#8984)

tests/cpp/objective/test_lambdarank_obj.h

@@ -0,0 +1,26 @@
+/**
+ * Copyright 2023, XGBoost Contributors
+ */
+#ifndef XGBOOST_OBJECTIVE_TEST_LAMBDARANK_OBJ_H_
+#define XGBOOST_OBJECTIVE_TEST_LAMBDARANK_OBJ_H_
+#include <gtest/gtest.h>
+#include <xgboost/data.h>                           // for MetaInfo
+#include <xgboost/host_device_vector.h>             // for HostDeviceVector
+#include <xgboost/linalg.h>                         // for All
+#include <xgboost/objective.h>                      // for ObjFunction
+
+#include <memory>                                   // for shared_ptr, make_shared
+#include <numeric>                                  // for iota
+#include <vector>                                   // for vector
+
+#include "../../../src/common/ranking_utils.h"      // for LambdaRankParam, MAPCache
+#include "../../../src/objective/lambdarank_obj.h"  // for MAPStat
+#include "../helpers.h"                             // for EmptyDMatrix
+
+namespace xgboost::obj {
+/**
+ * \brief Initialize test data for make pair tests.
+ */
+void InitMakePairTest(Context const* ctx, MetaInfo* out_info, HostDeviceVector<float>* out_predt);
+}  // namespace xgboost::obj
+#endif  // XGBOOST_OBJECTIVE_TEST_LAMBDARANK_OBJ_H_