Tests: move tests from USD test directory into `io/common` and `io/usd`

This commit is a followup of {D7649}, and ports the USD tests to the new
testing approach. It moves test code from `tests/gtests/usd` into
`source/blender/io/common` and `source/blender/io/usd`, and adjusts the
use of namespaces to be consistent with the other tests.

I decided to put one test into `io/usd/tests`, instead of
`io/usd/intern`. The reason is that this test does not correspond with a
single file in that directory; instead, it tests Blender's integration
with the USD library itself.

There are two new CLI arguments for the Big Test Runner:

- `--test-assets-dir`, which points to the `lib/tests` directory in the
  SVN repository. This allows unit tests to find test assets.
- `--test-release-dir`, which points to `bin/{BLENDER_VERSION}` in the
  build directory. At the moment this is only used by the USD test.

The CLI arguments are automatically passed to the Big Test Runner when
using `ctest`. When manually running the tests, the arguments are only
required when there is a test run that needs them.

For more info about splitting some code into 'common', see
rB084c5d6c7e2cf8.

No functional changes to the tests themselves, only to the way they are
built & run.

Differential Revision: https://developer.blender.org/D8314

Reviewed by: brecht, mont29

4 files changed, 695 insertions, 0 deletions

diff --git a/source/blender/io/common/CMakeLists.txt b/source/blender/io/common/CMakeLists.txt
index 708f24ca0e2..a6975863413 100644
--- a/source/blender/io/common/CMakeLists.txt
+++ b/source/blender/io/common/CMakeLists.txt
@@ -48,3 +48,16 @@ set(LIB
 blender_add_lib(bf_io_common "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
 
 target_link_libraries(bf_io_common INTERFACE)
+
+if(WITH_GTESTS)
+  set(TEST_SRC
+    intern/abstract_hierarchy_iterator_test.cc
+    intern/hierarchy_context_order_test.cc
+    intern/object_identifier_test.cc
+  )
+  set(TEST_LIB
+    bf_blenloader_test
+  )
+  include(GTestTesting)
+  blender_add_test_lib(bf_io_common_tests "${TEST_SRC}" "${INC};${TEST_INC}" "${INC_SYS}" "${LIB};${TEST_LIB}")
+endif()
diff --git a/source/blender/io/common/intern/abstract_hierarchy_iterator_test.cc b/source/blender/io/common/intern/abstract_hierarchy_iterator_test.cc
new file mode 100644
index 00000000000..04d26422143
--- /dev/null
+++ b/source/blender/io/common/intern/abstract_hierarchy_iterator_test.cc
@@ -0,0 +1,319 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2019 Blender Foundation.
+ * All rights reserved.
+ */
+#include "IO_abstract_hierarchy_iterator.h"
+#include "blenloader/blendfile_loading_base_test.h"
+
+#include "BLI_math.h"
+#include "DEG_depsgraph.h"
+#include "DNA_object_types.h"
+
+#include <map>
+#include <set>
+
+namespace blender::io {
+
+namespace {
+
+/* Mapping from ID.name to set of export hierarchy path. Duplicated objects can be exported
+ * multiple times with different export paths, hence the set. */
+typedef std::map<std::string, std::set<std::string>> used_writers;
+
+class TestHierarchyWriter : public AbstractHierarchyWriter {
+ public:
+  std::string writer_type;
+  used_writers &writers_map;
+
+  TestHierarchyWriter(const std::string &writer_type, used_writers &writers_map)
+      : writer_type(writer_type), writers_map(writers_map)
+  {
+  }
+
+  void write(HierarchyContext &context) override
+  {
+    const char *id_name = context.object->id.name;
+    used_writers::mapped_type &writers = writers_map[id_name];
+
+    if (writers.find(context.export_path) != writers.end()) {
+      ADD_FAILURE() << "Unexpectedly found another " << writer_type << " writer for " << id_name
+                    << " to export to " << context.export_path;
+    }
+    writers.insert(context.export_path);
+  }
+};
+
+}  // namespace
+
+class TestingHierarchyIterator : public AbstractHierarchyIterator {
+ public: /* Public so that the test cases can directly inspect the created writers. */
+  used_writers transform_writers;
+  used_writers data_writers;
+  used_writers hair_writers;
+  used_writers particle_writers;
+
+ public:
+  explicit TestingHierarchyIterator(Depsgraph *depsgraph) : AbstractHierarchyIterator(depsgraph)
+  {
+  }
+  virtual ~TestingHierarchyIterator()
+  {
+  }
+
+ protected:
+  AbstractHierarchyWriter *create_transform_writer(const HierarchyContext * /*context*/) override
+  {
+    return new TestHierarchyWriter("transform", transform_writers);
+  }
+  AbstractHierarchyWriter *create_data_writer(const HierarchyContext * /*context*/) override
+  {
+    return new TestHierarchyWriter("data", data_writers);
+  }
+  AbstractHierarchyWriter *create_hair_writer(const HierarchyContext * /*context*/) override
+  {
+    return new TestHierarchyWriter("hair", hair_writers);
+  }
+  AbstractHierarchyWriter *create_particle_writer(const HierarchyContext * /*context*/) override
+  {
+    return new TestHierarchyWriter("particle", particle_writers);
+  }
+
+  void delete_object_writer(AbstractHierarchyWriter *writer) override
+  {
+    delete writer;
+  }
+};
+
+class USDHierarchyIteratorTest : public BlendfileLoadingBaseTest {
+ protected:
+  TestingHierarchyIterator *iterator;
+
+  virtual void SetUp()
+  {
+    BlendfileLoadingBaseTest::SetUp();
+    iterator = nullptr;
+  }
+
+  virtual void TearDown()
+  {
+    iterator_free();
+    BlendfileLoadingBaseTest::TearDown();
+  }
+
+  /* Create a test iterator. */
+  void iterator_create()
+  {
+    iterator = new TestingHierarchyIterator(depsgraph);
+  }
+  /* Free the test iterator if it is not nullptr. */
+  void iterator_free()
+  {
+    if (iterator == nullptr) {
+      return;
+    }
+    delete iterator;
+    iterator = nullptr;
+  }
+};
+
+TEST_F(USDHierarchyIteratorTest, ExportHierarchyTest)
+{
+  /* Load the test blend file. */
+  if (!blendfile_load("usd/usd_hierarchy_export_test.blend")) {
+    return;
+  }
+  depsgraph_create(DAG_EVAL_RENDER);
+  iterator_create();
+
+  iterator->iterate_and_write();
+
+  // Mapping from object name to set of export paths.
+  used_writers expected_transforms = {
+      {"OBCamera", {"/Camera"}},
+      {"OBDupli1", {"/Dupli1"}},
+      {"OBDupli2", {"/ParentOfDupli2/Dupli2"}},
+      {"OBGEO_Ear_L",
+       {"/Dupli1/GEO_Head-0/GEO_Ear_L-1",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Ear_L",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Ear_L-1"}},
+      {"OBGEO_Ear_R",
+       {"/Dupli1/GEO_Head-0/GEO_Ear_R-2",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Ear_R",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Ear_R-2"}},
+      {"OBGEO_Head",
+       {"/Dupli1/GEO_Head-0",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0"}},
+      {"OBGEO_Nose",
+       {"/Dupli1/GEO_Head-0/GEO_Nose-3",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Nose",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Nose-3"}},
+      {"OBGround plane", {"/Ground plane"}},
+      {"OBOutsideDupliGrandParent", {"/Ground plane/OutsideDupliGrandParent"}},
+      {"OBOutsideDupliParent", {"/Ground plane/OutsideDupliGrandParent/OutsideDupliParent"}},
+      {"OBParentOfDupli2", {"/ParentOfDupli2"}}};
+  EXPECT_EQ(expected_transforms, iterator->transform_writers);
+
+  used_writers expected_data = {
+      {"OBCamera", {"/Camera/Camera"}},
+      {"OBGEO_Ear_L",
+       {"/Dupli1/GEO_Head-0/GEO_Ear_L-1/Ear",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Ear_L/Ear",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Ear_L-1/Ear"}},
+      {"OBGEO_Ear_R",
+       {"/Dupli1/GEO_Head-0/GEO_Ear_R-2/Ear",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Ear_R/Ear",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Ear_R-2/Ear"}},
+      {"OBGEO_Head",
+       {"/Dupli1/GEO_Head-0/Face",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/Face",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/Face"}},
+      {"OBGEO_Nose",
+       {"/Dupli1/GEO_Head-0/GEO_Nose-3/Nose",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Nose/Nose",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Nose-3/Nose"}},
+      {"OBGround plane", {"/Ground plane/Plane"}},
+      {"OBParentOfDupli2", {"/ParentOfDupli2/Icosphere"}},
+  };
+
+  EXPECT_EQ(expected_data, iterator->data_writers);
+
+  // The scene has no hair or particle systems.
+  EXPECT_EQ(0, iterator->hair_writers.size());
+  EXPECT_EQ(0, iterator->particle_writers.size());
+
+  // On the second iteration, everything should be written as well.
+  // This tests the default value of iterator->export_subset_.
+  iterator->transform_writers.clear();
+  iterator->data_writers.clear();
+  iterator->iterate_and_write();
+  EXPECT_EQ(expected_transforms, iterator->transform_writers);
+  EXPECT_EQ(expected_data, iterator->data_writers);
+}
+
+TEST_F(USDHierarchyIteratorTest, ExportSubsetTest)
+{
+  // The scene has no hair or particle systems, and this is already covered by ExportHierarchyTest,
+  // so not included here. Update this test when hair & particle systems are included.
+
+  /* Load the test blend file. */
+  if (!blendfile_load("usd/usd_hierarchy_export_test.blend")) {
+    return;
+  }
+  depsgraph_create(DAG_EVAL_RENDER);
+  iterator_create();
+
+  // Mapping from object name to set of export paths.
+  used_writers expected_transforms = {
+      {"OBCamera", {"/Camera"}},
+      {"OBDupli1", {"/Dupli1"}},
+      {"OBDupli2", {"/ParentOfDupli2/Dupli2"}},
+      {"OBGEO_Ear_L",
+       {"/Dupli1/GEO_Head-0/GEO_Ear_L-1",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Ear_L",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Ear_L-1"}},
+      {"OBGEO_Ear_R",
+       {"/Dupli1/GEO_Head-0/GEO_Ear_R-2",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Ear_R",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Ear_R-2"}},
+      {"OBGEO_Head",
+       {"/Dupli1/GEO_Head-0",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0"}},
+      {"OBGEO_Nose",
+       {"/Dupli1/GEO_Head-0/GEO_Nose-3",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Nose",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Nose-3"}},
+      {"OBGround plane", {"/Ground plane"}},
+      {"OBOutsideDupliGrandParent", {"/Ground plane/OutsideDupliGrandParent"}},
+      {"OBOutsideDupliParent", {"/Ground plane/OutsideDupliGrandParent/OutsideDupliParent"}},
+      {"OBParentOfDupli2", {"/ParentOfDupli2"}}};
+
+  used_writers expected_data = {
+      {"OBCamera", {"/Camera/Camera"}},
+      {"OBGEO_Ear_L",
+       {"/Dupli1/GEO_Head-0/GEO_Ear_L-1/Ear",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Ear_L/Ear",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Ear_L-1/Ear"}},
+      {"OBGEO_Ear_R",
+       {"/Dupli1/GEO_Head-0/GEO_Ear_R-2/Ear",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Ear_R/Ear",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Ear_R-2/Ear"}},
+      {"OBGEO_Head",
+       {"/Dupli1/GEO_Head-0/Face",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/Face",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/Face"}},
+      {"OBGEO_Nose",
+       {"/Dupli1/GEO_Head-0/GEO_Nose-3/Nose",
+        "/Ground plane/OutsideDupliGrandParent/OutsideDupliParent/GEO_Head/GEO_Nose/Nose",
+        "/ParentOfDupli2/Dupli2/GEO_Head-0/GEO_Nose-3/Nose"}},
+      {"OBGround plane", {"/Ground plane/Plane"}},
+      {"OBParentOfDupli2", {"/ParentOfDupli2/Icosphere"}},
+  };
+
+  // Even when only asking an export of transforms, on the first frame everything should be
+  // exported.
+  {
+    ExportSubset export_subset = {0};
+    export_subset.transforms = true;
+    export_subset.shapes = false;
+    iterator->set_export_subset(export_subset);
+  }
+  iterator->iterate_and_write();
+  EXPECT_EQ(expected_transforms, iterator->transform_writers);
+  EXPECT_EQ(expected_data, iterator->data_writers);
+
+  // Clear data to prepare for the next iteration.
+  iterator->transform_writers.clear();
+  iterator->data_writers.clear();
+
+  // Second iteration, should only write transforms now.
+  iterator->iterate_and_write();
+  EXPECT_EQ(expected_transforms, iterator->transform_writers);
+  EXPECT_EQ(0, iterator->data_writers.size());
+
+  // Clear data to prepare for the next iteration.
+  iterator->transform_writers.clear();
+  iterator->data_writers.clear();
+
+  // Third iteration, should only write data now.
+  {
+    ExportSubset export_subset = {0};
+    export_subset.transforms = false;
+    export_subset.shapes = true;
+    iterator->set_export_subset(export_subset);
+  }
+  iterator->iterate_and_write();
+  EXPECT_EQ(0, iterator->transform_writers.size());
+  EXPECT_EQ(expected_data, iterator->data_writers);
+
+  // Clear data to prepare for the next iteration.
+  iterator->transform_writers.clear();
+  iterator->data_writers.clear();
+
+  // Fourth iteration, should export everything now.
+  {
+    ExportSubset export_subset = {0};
+    export_subset.transforms = true;
+    export_subset.shapes = true;
+    iterator->set_export_subset(export_subset);
+  }
+  iterator->iterate_and_write();
+  EXPECT_EQ(expected_transforms, iterator->transform_writers);
+  EXPECT_EQ(expected_data, iterator->data_writers);
+}
+}  // namespace blender::io
diff --git a/source/blender/io/common/intern/hierarchy_context_order_test.cc b/source/blender/io/common/intern/hierarchy_context_order_test.cc
new file mode 100644
index 00000000000..7273b92c479
--- /dev/null
+++ b/source/blender/io/common/intern/hierarchy_context_order_test.cc
@@ -0,0 +1,129 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2019 Blender Foundation.
+ * All rights reserved.
+ */
+#include "IO_abstract_hierarchy_iterator.h"
+
+#include "testing/testing.h"
+
+extern "C" {
+#include "BLI_utildefines.h"
+}
+
+namespace blender::io {
+
+namespace {
+
+Object *fake_pointer(int value)
+{
+  return static_cast<Object *>(POINTER_FROM_INT(value));
+}
+
+}  // namespace
+
+class HierarchyContextOrderTest : public testing::Test {
+};
+
+TEST_F(HierarchyContextOrderTest, ObjectPointerTest)
+{
+  HierarchyContext ctx_a = {0};
+  ctx_a.object = fake_pointer(1);
+  ctx_a.duplicator = nullptr;
+
+  HierarchyContext ctx_b = {0};
+  ctx_b.object = fake_pointer(2);
+  ctx_b.duplicator = nullptr;
+
+  EXPECT_LT(ctx_a, ctx_b);
+  EXPECT_FALSE(ctx_b < ctx_a);
+  EXPECT_FALSE(ctx_a < ctx_a);
+}
+
+TEST_F(HierarchyContextOrderTest, DuplicatorPointerTest)
+{
+  HierarchyContext ctx_a = {0};
+  ctx_a.object = fake_pointer(1);
+  ctx_a.duplicator = fake_pointer(1);
+  ctx_a.export_name = "A";
+
+  HierarchyContext ctx_b = {0};
+  ctx_b.object = fake_pointer(1);
+  ctx_b.duplicator = fake_pointer(1);
+  ctx_b.export_name = "B";
+
+  EXPECT_LT(ctx_a, ctx_b);
+  EXPECT_FALSE(ctx_b < ctx_a);
+  EXPECT_FALSE(ctx_a < ctx_a);
+}
+
+TEST_F(HierarchyContextOrderTest, ExportParentTest)
+{
+  HierarchyContext ctx_a = {0};
+  ctx_a.object = fake_pointer(1);
+  ctx_a.export_parent = fake_pointer(1);
+
+  HierarchyContext ctx_b = {0};
+  ctx_b.object = fake_pointer(1);
+  ctx_b.export_parent = fake_pointer(2);
+
+  EXPECT_LT(ctx_a, ctx_b);
+  EXPECT_FALSE(ctx_b < ctx_a);
+  EXPECT_FALSE(ctx_a < ctx_a);
+}
+
+TEST_F(HierarchyContextOrderTest, TransitiveTest)
+{
+  HierarchyContext ctx_a = {0};
+  ctx_a.object = fake_pointer(1);
+  ctx_a.export_parent = fake_pointer(1);
+  ctx_a.duplicator = nullptr;
+  ctx_a.export_name = "A";
+
+  HierarchyContext ctx_b = {0};
+  ctx_b.object = fake_pointer(2);
+  ctx_b.export_parent = nullptr;
+  ctx_b.duplicator = fake_pointer(1);
+  ctx_b.export_name = "B";
+
+  HierarchyContext ctx_c = {0};
+  ctx_c.object = fake_pointer(2);
+  ctx_c.export_parent = fake_pointer(2);
+  ctx_c.duplicator = fake_pointer(1);
+  ctx_c.export_name = "C";
+
+  HierarchyContext ctx_d = {0};
+  ctx_d.object = fake_pointer(2);
+  ctx_d.export_parent = fake_pointer(3);
+  ctx_d.duplicator = nullptr;
+  ctx_d.export_name = "D";
+
+  EXPECT_LT(ctx_a, ctx_b);
+  EXPECT_LT(ctx_a, ctx_c);
+  EXPECT_LT(ctx_a, ctx_d);
+  EXPECT_LT(ctx_b, ctx_c);
+  EXPECT_LT(ctx_b, ctx_d);
+  EXPECT_LT(ctx_c, ctx_d);
+
+  EXPECT_FALSE(ctx_b < ctx_a);
+  EXPECT_FALSE(ctx_c < ctx_a);
+  EXPECT_FALSE(ctx_d < ctx_a);
+  EXPECT_FALSE(ctx_c < ctx_b);
+  EXPECT_FALSE(ctx_d < ctx_b);
+  EXPECT_FALSE(ctx_d < ctx_c);
+}
+
+}  // namespace blender::io
diff --git a/source/blender/io/common/intern/object_identifier_test.cc b/source/blender/io/common/intern/object_identifier_test.cc
new file mode 100644
index 00000000000..2b565876f22
--- /dev/null
+++ b/source/blender/io/common/intern/object_identifier_test.cc
@@ -0,0 +1,234 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2019 Blender Foundation.
+ * All rights reserved.
+ */
+#include "IO_abstract_hierarchy_iterator.h"
+
+#include "testing/testing.h"
+
+#include "BLI_utildefines.h"
+
+#include <climits>
+
+namespace blender::io {
+
+namespace {
+
+/* Return object pointer for use in tests. This makes it possible to reliably test for
+ * order/equality functions while using hard-coded values for simplicity. */
+Object *fake_pointer(int value)
+{
+  return static_cast<Object *>(POINTER_FROM_INT(value));
+}
+
+/* PersistentID subclass for use in tests, making it easier to construct test values. */
+class TestPersistentID : public PersistentID {
+ public:
+  TestPersistentID(int value0,
+                   int value1,
+                   int value2,
+                   int value3,
+                   int value4,
+                   int value5,
+                   int value6,
+                   int value7)
+  {
+    persistent_id_[0] = value0;
+    persistent_id_[1] = value1;
+    persistent_id_[2] = value2;
+    persistent_id_[3] = value3;
+    persistent_id_[4] = value4;
+    persistent_id_[5] = value5;
+    persistent_id_[6] = value6;
+    persistent_id_[7] = value7;
+  }
+  TestPersistentID(int value0, int value1, int value2)
+      : TestPersistentID(value0, value1, value2, INT_MAX, INT_MAX, INT_MAX, INT_MAX, INT_MAX)
+  {
+  }
+  TestPersistentID(int value0, int value1) : TestPersistentID(value0, value1, INT_MAX)
+  {
+  }
+  explicit TestPersistentID(int value0) : TestPersistentID(value0, INT_MAX)
+  {
+  }
+};
+
+/* ObjectIdentifier subclass for use in tests, making it easier to construct test values. */
+class TestObjectIdentifier : public ObjectIdentifier {
+ public:
+  TestObjectIdentifier(Object *object, Object *duplicated_by, const PersistentID &persistent_id)
+      : ObjectIdentifier(object, duplicated_by, persistent_id)
+  {
+  }
+};
+
+}  // namespace
+
+class ObjectIdentifierOrderTest : public testing::Test {
+};
+
+TEST_F(ObjectIdentifierOrderTest, graph_root)
+{
+  ObjectIdentifier id_root_1 = ObjectIdentifier::for_graph_root();
+  ObjectIdentifier id_root_2 = ObjectIdentifier::for_graph_root();
+  EXPECT_TRUE(id_root_1 == id_root_2);
+  EXPECT_FALSE(id_root_1 < id_root_2);
+  EXPECT_FALSE(id_root_2 < id_root_1);
+
+  ObjectIdentifier id_a = ObjectIdentifier::for_real_object(fake_pointer(1));
+  EXPECT_FALSE(id_root_1 == id_a);
+  EXPECT_TRUE(id_root_1 < id_a);
+  EXPECT_FALSE(id_a < id_root_1);
+
+  ObjectIdentifier id_accidental_root = ObjectIdentifier::for_real_object(nullptr);
+  EXPECT_TRUE(id_root_1 == id_accidental_root);
+  EXPECT_FALSE(id_root_1 < id_accidental_root);
+  EXPECT_FALSE(id_accidental_root < id_root_1);
+}
+
+TEST_F(ObjectIdentifierOrderTest, real_objects)
+{
+  ObjectIdentifier id_a = ObjectIdentifier::for_real_object(fake_pointer(1));
+  ObjectIdentifier id_b = ObjectIdentifier::for_real_object(fake_pointer(2));
+  EXPECT_FALSE(id_a == id_b);
+  EXPECT_TRUE(id_a < id_b);
+}
+
+TEST_F(ObjectIdentifierOrderTest, duplicated_objects)
+{
+  ObjectIdentifier id_real_a = ObjectIdentifier::for_real_object(fake_pointer(1));
+  TestObjectIdentifier id_dupli_a(fake_pointer(1), fake_pointer(2), TestPersistentID(0));
+  TestObjectIdentifier id_dupli_b(fake_pointer(1), fake_pointer(3), TestPersistentID(0));
+  TestObjectIdentifier id_different_dupli_b(fake_pointer(1), fake_pointer(3), TestPersistentID(1));
+
+  EXPECT_FALSE(id_real_a == id_dupli_a);
+  EXPECT_FALSE(id_dupli_a == id_dupli_b);
+  EXPECT_TRUE(id_real_a < id_dupli_a);
+  EXPECT_TRUE(id_real_a < id_dupli_b);
+  EXPECT_TRUE(id_dupli_a < id_dupli_b);
+  EXPECT_TRUE(id_dupli_a < id_different_dupli_b);
+
+  EXPECT_FALSE(id_dupli_b == id_different_dupli_b);
+  EXPECT_FALSE(id_dupli_a == id_different_dupli_b);
+  EXPECT_TRUE(id_dupli_b < id_different_dupli_b);
+  EXPECT_FALSE(id_different_dupli_b < id_dupli_b);
+}
+
+TEST_F(ObjectIdentifierOrderTest, behaviour_as_map_keys)
+{
+  ObjectIdentifier id_root = ObjectIdentifier::for_graph_root();
+  ObjectIdentifier id_another_root = ObjectIdentifier::for_graph_root();
+  ObjectIdentifier id_real_a = ObjectIdentifier::for_real_object(fake_pointer(1));
+  TestObjectIdentifier id_dupli_a(fake_pointer(1), fake_pointer(2), TestPersistentID(0));
+  TestObjectIdentifier id_dupli_b(fake_pointer(1), fake_pointer(3), TestPersistentID(0));
+  AbstractHierarchyIterator::ExportGraph graph;
+
+  /* This inserts the keys with default values. */
+  graph[id_root];
+  graph[id_real_a];
+  graph[id_dupli_a];
+  graph[id_dupli_b];
+  graph[id_another_root];
+
+  EXPECT_EQ(4, graph.size());
+
+  graph.erase(id_another_root);
+  EXPECT_EQ(3, graph.size());
+
+  TestObjectIdentifier id_another_dupli_b(fake_pointer(1), fake_pointer(3), TestPersistentID(0));
+  graph.erase(id_another_dupli_b);
+  EXPECT_EQ(2, graph.size());
+}
+
+TEST_F(ObjectIdentifierOrderTest, map_copy_and_update)
+{
+  ObjectIdentifier id_root = ObjectIdentifier::for_graph_root();
+  ObjectIdentifier id_real_a = ObjectIdentifier::for_real_object(fake_pointer(1));
+  TestObjectIdentifier id_dupli_a(fake_pointer(1), fake_pointer(2), TestPersistentID(0));
+  TestObjectIdentifier id_dupli_b(fake_pointer(1), fake_pointer(3), TestPersistentID(0));
+  TestObjectIdentifier id_dupli_c(fake_pointer(1), fake_pointer(3), TestPersistentID(1));
+  AbstractHierarchyIterator::ExportGraph graph;
+
+  /* This inserts the keys with default values. */
+  graph[id_root];
+  graph[id_real_a];
+  graph[id_dupli_a];
+  graph[id_dupli_b];
+  graph[id_dupli_c];
+  EXPECT_EQ(5, graph.size());
+
+  AbstractHierarchyIterator::ExportGraph graph_copy = graph;
+  EXPECT_EQ(5, graph_copy.size());
+
+  // Updating a value in a copy should not update the original.
+  HierarchyContext ctx1;
+  HierarchyContext ctx2;
+  ctx1.object = fake_pointer(1);
+  ctx2.object = fake_pointer(2);
+
+  graph_copy[id_root].insert(&ctx1);
+  EXPECT_EQ(0, graph[id_root].size());
+
+  // Deleting a key in the copy should not update the original.
+  graph_copy.erase(id_dupli_c);
+  EXPECT_EQ(4, graph_copy.size());
+  EXPECT_EQ(5, graph.size());
+}
+
+class PersistentIDTest : public testing::Test {
+};
+
+TEST_F(PersistentIDTest, is_from_same_instancer)
+{
+  PersistentID child_id_a = TestPersistentID(42, 327);
+  PersistentID child_id_b = TestPersistentID(17, 327);
+  PersistentID child_id_c = TestPersistentID(17);
+
+  EXPECT_TRUE(child_id_a.is_from_same_instancer_as(child_id_b));
+  EXPECT_FALSE(child_id_a.is_from_same_instancer_as(child_id_c));
+}
+
+TEST_F(PersistentIDTest, instancer_id)
+{
+  PersistentID child_id = TestPersistentID(42, 327);
+
+  PersistentID expect_instancer_id = TestPersistentID(327);
+  EXPECT_EQ(expect_instancer_id, child_id.instancer_pid());
+
+  PersistentID empty_id;
+  EXPECT_EQ(empty_id, child_id.instancer_pid().instancer_pid());
+
+  EXPECT_LT(child_id, expect_instancer_id);
+  EXPECT_LT(expect_instancer_id, empty_id);
+}
+
+TEST_F(PersistentIDTest, as_object_name_suffix)
+{
+  EXPECT_EQ("", PersistentID().as_object_name_suffix());
+  EXPECT_EQ("47", TestPersistentID(47).as_object_name_suffix());
+  EXPECT_EQ("327-47", TestPersistentID(47, 327).as_object_name_suffix());
+  EXPECT_EQ("42-327-47", TestPersistentID(47, 327, 42).as_object_name_suffix());
+
+  EXPECT_EQ("7-6-5-4-3-2-1-0", TestPersistentID(0, 1, 2, 3, 4, 5, 6, 7).as_object_name_suffix());
+
+  EXPECT_EQ("0-0-0", TestPersistentID(0, 0, 0).as_object_name_suffix());
+  EXPECT_EQ("0-0", TestPersistentID(0, 0).as_object_name_suffix());
+  EXPECT_EQ("-3--2--1", TestPersistentID(-1, -2, -3).as_object_name_suffix());
+}
+
+}  // namespace blender::io