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

source/blender/io/usd/CMakeLists.txt

@@ -109,3 +109,15 @@ else()
 endif()
 
 target_link_libraries(bf_usd INTERFACE ${TBB_LIBRARIES})
+
+if(WITH_GTESTS)
+  set(TEST_SRC
+    tests/usd_stage_creation_test.cc
+  )
+  set(TEST_INC
+  )
+  set(TEST_LIB
+  )
+  include(GTestTesting)
+  blender_add_test_lib(bf_io_usd_tests "${TEST_SRC}" "${INC};${TEST_INC}" "${INC_SYS}" "${LIB};${TEST_LIB}")
+endif()

source/blender/io/usd/tests/usd_stage_creation_test.cc

@@ -0,0 +1,68 @@
+/*
+ * 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 "testing/testing.h"
+#include <pxr/usd/usd/stage.h>
+
+#include <string>
+
+#include "BLI_path_util.h"
+#include "BLI_utildefines.h"
+
+#include "BKE_appdir.h"
+
+extern "C" {
+/* Workaround to make it possible to pass a path at runtime to USD. See creator.c. */
+void usd_initialise_plugin_path(const char *datafiles_usd_path);
+}
+
+namespace blender::io::usd {
+
+class USDStageCreationTest : public testing::Test {
+};
+
+TEST_F(USDStageCreationTest, JSONFileLoadingTest)
+{
+  const std::string &release_dir = blender::tests::flags_test_release_dir();
+  if (release_dir.empty()) {
+    FAIL();
+  }
+
+  char usd_datafiles_dir[FILE_MAX];
+  BLI_path_join(usd_datafiles_dir, FILE_MAX, release_dir.c_str(), "datafiles", "usd", nullptr);
+
+  usd_initialise_plugin_path(usd_datafiles_dir);
+
+  /* Simply the ability to create a USD Stage for a specific filename means that the extension
+   * has been recognised by the USD library, and that a USD plugin has been loaded to write such
+   * files. Practically, this is a test to see whether the USD JSON files can be found and
+   * loaded. */
+  std::string filename = "usd-stage-creation-test.usdc";
+  pxr::UsdStageRefPtr usd_stage = pxr::UsdStage::CreateNew(filename);
+  if (usd_stage != nullptr) {
+    /* Even though we don't call usd_stage->SaveFile(), a file is still created on the filesystem
+     * when we call CreateNew(). It's immediately closed, though, so we can safely call unlink()
+     * here. */
+    unlink(filename.c_str());
+  }
+  else {
+    FAIL() << "unable to find suitable USD plugin to write " << filename;
+  }
+}
+
+}  // namespace blender::io::usd