GH-48682: [C++] Remove IPC dependency from array_union_test.cc by moving MakeUnion to testing utilities

cpp/src/arrow/array/array_union_test.cc

@@ -22,8 +22,6 @@
 #include "arrow/array.h"
 #include "arrow/array/builder_nested.h"
 #include "arrow/array/builder_union.h"
-// TODO ipc shouldn't be included here
-#include "arrow/ipc/test_common.h"
 #include "arrow/testing/builder.h"
 #include "arrow/testing/gtest_util.h"
 #include "arrow/testing/util.h"
@@ -37,7 +35,7 @@ using internal::checked_pointer_cast;
 
 TEST(TestUnionArray, TestSliceEquals) {
   std::shared_ptr<RecordBatch> batch;
-  ASSERT_OK(ipc::test::MakeUnion(&batch));
+  ASSERT_OK(MakeUnion(&batch));
 
   auto CheckUnion = [](std::shared_ptr<Array> array) {
     const int64_t size = array->length();

cpp/src/arrow/integration/json_integration_test.cc

@@ -927,7 +927,7 @@ TEST(TestJsonArrayWriter, NestedTypes) {
 
 TEST(TestJsonArrayWriter, Unions) {
   std::shared_ptr<RecordBatch> batch;
-  ASSERT_OK(MakeUnion(&batch));
+  ASSERT_OK(ipc::test::MakeUnion(&batch));
 
   for (int i = 0; i < batch->num_columns(); ++i) {
     TestArrayRoundTrip(*batch->column(i));
@@ -1155,7 +1155,7 @@ const std::vector<ipc::test::MakeRecordBatch*> kBatchCases = {
     &MakeDeeplyNestedListView,
     &MakeStringTypesRecordBatchWithNulls,
     &MakeStruct,
-    &MakeUnion,
+    &ipc::test::MakeUnion,
     &MakeDictionary,
     &MakeNestedDictionary,
     &MakeMap,

cpp/src/arrow/ipc/test_common.cc

@@ -670,55 +670,8 @@ Status MakeRunEndEncoded(std::shared_ptr<RecordBatch>* out) {
 }
 
 Status MakeUnion(std::shared_ptr<RecordBatch>* out) {
-  // Define schema
-  std::vector<std::shared_ptr<Field>> union_fields(
-      {field("u0", int32()), field("u1", uint8())});
-
-  std::vector<int8_t> type_codes = {5, 10};
-  auto sparse_type = sparse_union(union_fields, type_codes);
-  auto dense_type = dense_union(union_fields, type_codes);
-
-  auto f0 = field("sparse", sparse_type);
-  auto f1 = field("dense", dense_type);
-
-  auto schema = ::arrow::schema({f0, f1});
-
-  // Create data
-  std::vector<std::shared_ptr<Array>> sparse_children(2);
-  std::vector<std::shared_ptr<Array>> dense_children(2);
-
-  const int64_t length = 7;
-
-  std::shared_ptr<Buffer> type_ids_buffer;
-  std::vector<uint8_t> type_ids = {5, 10, 5, 5, 10, 10, 5};
-  RETURN_NOT_OK(CopyBufferFromVector(type_ids, default_memory_pool(), &type_ids_buffer));
-
-  std::vector<int32_t> u0_values = {0, 1, 2, 3, 4, 5, 6};
-  ArrayFromVector<Int32Type, int32_t>(u0_values, &sparse_children[0]);
-
-  std::vector<uint8_t> u1_values = {10, 11, 12, 13, 14, 15, 16};
-  ArrayFromVector<UInt8Type, uint8_t>(u1_values, &sparse_children[1]);
-
-  // dense children
-  u0_values = {0, 2, 3, 7};
-  ArrayFromVector<Int32Type, int32_t>(u0_values, &dense_children[0]);
-
-  u1_values = {11, 14, 15};
-  ArrayFromVector<UInt8Type, uint8_t>(u1_values, &dense_children[1]);
-
-  std::shared_ptr<Buffer> offsets_buffer;
-  std::vector<int32_t> offsets = {0, 0, 1, 2, 1, 2, 3};
-  RETURN_NOT_OK(CopyBufferFromVector(offsets, default_memory_pool(), &offsets_buffer));
-
-  auto sparse = std::make_shared<SparseUnionArray>(sparse_type, length, sparse_children,
-                                                   type_ids_buffer);
-  auto dense = std::make_shared<DenseUnionArray>(dense_type, length, dense_children,
-                                                 type_ids_buffer, offsets_buffer);
-
-  // construct batch
-  std::vector<std::shared_ptr<Array>> arrays = {sparse, dense};
-  *out = RecordBatch::Make(schema, length, arrays);
-  return Status::OK();
+  // Delegate to the shared implementation in arrow::testing::util
+  return ::arrow::MakeUnion(out);
 }
 
 Status MakeDictionary(std::shared_ptr<RecordBatch>* out) {

cpp/src/arrow/testing/util.cc

@@ -39,8 +39,11 @@
 #  include <unistd.h>      // IWYU pragma: keep
 #endif
 
+#include "arrow/array.h"
+#include "arrow/array/builder_union.h"
 #include "arrow/config.h"
 #include "arrow/table.h"
+#include "arrow/testing/builder.h"
 #include "arrow/testing/random.h"
 #include "arrow/type.h"
 #include "arrow/util/cpu_info.h"
@@ -242,4 +245,55 @@ std::vector<int64_t> GetSupportedHardwareFlags(
   return hardware_flags;
 }
 
+Status MakeUnion(std::shared_ptr<RecordBatch>* out) {
+  // Define schema
+  std::vector<std::shared_ptr<Field>> union_fields(
+      {field("u0", int32()), field("u1", uint8())});
+
+  std::vector<int8_t> type_codes = {5, 10};
+  auto sparse_type = sparse_union(union_fields, type_codes);
+  auto dense_type = dense_union(union_fields, type_codes);
+
+  auto f0 = field("sparse", sparse_type);
+  auto f1 = field("dense", dense_type);
+  auto schema = ::arrow::schema({f0, f1});
+
+  // Create data
+  std::vector<std::shared_ptr<Array>> sparse_children(2);
+  std::vector<std::shared_ptr<Array>> dense_children(2);
+
+  const int64_t length = 7;
+
+  std::shared_ptr<Buffer> type_ids_buffer;
+  std::vector<uint8_t> type_ids = {5, 10, 5, 5, 10, 10, 5};
+  RETURN_NOT_OK(CopyBufferFromVector(type_ids, default_memory_pool(), &type_ids_buffer));
+
+  std::vector<int32_t> u0_values = {0, 1, 2, 3, 4, 5, 6};
+  ArrayFromVector<Int32Type, int32_t>(u0_values, &sparse_children[0]);
+
+  std::vector<uint8_t> u1_values = {10, 11, 12, 13, 14, 15, 16};
+  ArrayFromVector<UInt8Type, uint8_t>(u1_values, &sparse_children[1]);
+
+  // dense children
+  u0_values = {0, 2, 3, 7};
+  ArrayFromVector<Int32Type, int32_t>(u0_values, &dense_children[0]);
+
+  u1_values = {11, 14, 15};
+  ArrayFromVector<UInt8Type, uint8_t>(u1_values, &dense_children[1]);
+
+  std::shared_ptr<Buffer> offsets_buffer;
+  std::vector<int32_t> offsets = {0, 0, 1, 2, 1, 2, 3};
+  RETURN_NOT_OK(CopyBufferFromVector(offsets, default_memory_pool(), &offsets_buffer));
+
+  auto sparse = std::make_shared<SparseUnionArray>(sparse_type, length, sparse_children,
+                                                   type_ids_buffer);
+  auto dense = std::make_shared<DenseUnionArray>(dense_type, length, dense_children,
+                                                 type_ids_buffer, offsets_buffer);
+
+  // construct batch
+  std::vector<std::shared_ptr<Array>> arrays = {sparse, dense};
+  *out = RecordBatch::Make(schema, length, arrays);
+  return Status::OK();
+}
+
 }  // namespace arrow

cpp/src/arrow/testing/util.h

@@ -142,4 +142,10 @@ ARROW_TESTING_EXPORT
 std::vector<int64_t> GetSupportedHardwareFlags(
     const std::vector<int64_t>& candidate_flags);
 
+// Creates a RecordBatch containing both sparse and dense union arrays with the same
+// union type definition. The union type has two fields: "u0" (int32) and "u1" (uint8)
+// with type codes 5 and 10 respectively. Both arrays have length 7.
+ARROW_TESTING_EXPORT
+Status MakeUnion(std::shared_ptr<RecordBatch>* out);
+
 }  // namespace arrow