Layers: Unittesting - make them granular

Some tests may break Blender, which makes the entire unittest routine to fail.
They are now I isolate the tests into individual files

Kudos to Sybren Stüvel and Sergey Sharybin for the advice.

Note: at the moment test_link.py is failing (since a41bbfb7)

tests/python/render_layer/test_object_delete.py

@@ -0,0 +1,104 @@
+# ./blender.bin --background -noaudio --python tests/python/render_layer/test_scene_copy.py -- --testdir="/data/lib/tests/"
+
+# ############################################################
+# Importing - Same For All Render Layer Tests
+# ############################################################
+
+import unittest
+
+import os, sys
+sys.path.append(os.path.dirname(__file__))
+
+from render_layer_common import *
+
+
+# ############################################################
+# Testing
+# ############################################################
+
+class UnitTesting(RenderLayerTesting):
+    def do_object_delete(self, del_mode):
+        import bpy
+        import os
+        import tempfile
+        import filecmp
+
+        ROOT = self.get_root()
+        with tempfile.TemporaryDirectory() as dirpath:
+            filepath_layers = os.path.join(ROOT, 'layers.blend')
+            filepath_reference_json = os.path.join(ROOT, 'layers_object_delete.json')
+
+            # open file
+            bpy.ops.wm.open_mainfile('EXEC_DEFAULT', filepath=filepath_layers)
+
+            # create sub-collections
+            three_b = bpy.data.objects.get('T.3b')
+            three_d = bpy.data.objects.get('T.3d')
+
+            scene = bpy.context.scene
+
+            # mangle the file a bit with some objects linked across collections
+            subzero = scene.master_collection.collections['1'].collections.new('sub-zero')
+            scorpion = subzero.collections.new('scorpion')
+            subzero.objects.link(three_d)
+            scorpion.objects.link(three_b)
+            scorpion.objects.link(three_d)
+
+            # object to delete
+            ob = three_d
+
+            # delete object
+            if del_mode == 'DATA':
+                bpy.data.objects.remove(ob, do_unlink=True)
+
+            elif del_mode == 'OPERATOR':
+                bpy.ops.object.select_all(action='DESELECT')
+                ob.select_set(action='SELECT')
+                bpy.ops.object.delete()
+
+            # save file
+            filepath_generated = os.path.join(dirpath, 'generated.blend')
+            bpy.ops.wm.save_mainfile('EXEC_DEFAULT', filepath=filepath_generated)
+
+            # get the generated json
+            datas = query_scene(filepath_generated, 'Main', (get_scene_collections, get_layers))
+            self.assertTrue(datas, "Data is not valid")
+
+            filepath_generated_json = os.path.join(dirpath, "generated.json")
+            with open(filepath_generated_json, "w") as f:
+                for data in datas:
+                    f.write(dump(data))
+
+            self.assertTrue(compare_files(
+                filepath_generated_json,
+                filepath_reference_json,
+                ),
+                "Scene dump files differ")
+
+    def test_object_delete_data(self):
+        """
+        See if objects are removed correctly from all related collections
+        bpy.data.objects.remove()
+        """
+        self.do_object_delete('DATA')
+
+    def test_object_delete_operator(self):
+        """
+        See if new objects are added to the correct collection
+        bpy.ops.object.del()
+        """
+        self.do_object_delete('OPERATOR')
+
+
+# ############################################################
+# Main - Same For All Render Layer Tests
+# ############################################################
+
+if __name__ == '__main__':
+    import sys
+
+    extra_arguments = sys.argv[sys.argv.index("--") + 1:] if "--" in sys.argv else []
+    sys.argv = [__file__] + (sys.argv[sys.argv.index("--") + 2:] if "--" in sys.argv else [])
+
+    UnitTesting._extra_arguments = extra_arguments
+    unittest.main()