Anim: add test for `bone_collection.bones`

Add Python test for access to `bone_collection.bones`.

tests/python/bl_animation_armature.py

@@ -29,17 +29,36 @@ class BoneCollectionTest(unittest.TestCase):
 
         return arm_ob, arm
 
-    def add_bones(self, arm_ob: bpy.types.Object) -> None:
-        # Switch to edit mode to add some bones.
+    def add_bones(self, arm_ob: bpy.types.Object) -> dict[str, bpy.types.Bone]:
+        """Add some test bones to the armature."""
 
+        # Switch to edit mode to add some bones.
         bpy.context.view_layer.objects.active = arm_ob
         bpy.ops.object.mode_set(mode='EDIT')
+        self.assertEqual('EDIT', arm_ob.mode, 'Armature should be in edit mode now')
 
+        arm = arm_ob.data
+        bone_names = ('root', 'child_L', 'child_R', 'child_L_L', 'child_L_R', 'child_R_L', 'child_R_R')
         try:
-            pass
+            for bone_name in bone_names:
+                ebone = arm.edit_bones.new(name=bone_name)
+                # Bones have to have a length, or they will be removed when exiting edit mode.
+                ebone.tail = (1, 0, 0)
+
+            arm.edit_bones['child_L'].parent = arm.edit_bones['root']
+            arm.edit_bones['child_R'].parent = arm.edit_bones['root']
+            arm.edit_bones['child_L_L'].parent = arm.edit_bones['child_L']
+            arm.edit_bones['child_L_R'].parent = arm.edit_bones['child_L']
+            arm.edit_bones['child_R_L'].parent = arm.edit_bones['child_R']
+            arm.edit_bones['child_R_R'].parent = arm.edit_bones['child_R']
+
         finally:
             bpy.ops.object.mode_set(mode='OBJECT')
 
+        # Return the bones, not the editbones.
+        return {bone_name: arm.bones[bone_name]
+                for bone_name in bone_names}
+
     def test_bone_collection_api(self):
         # Just to keep the rest of the code shorter.
         bcolls = self.arm.collections
@@ -92,6 +111,30 @@ class BoneCollectionTest(unittest.TestCase):
         # Check the array order.
         self.assertEqual([root1, r1_child1, root2, r1_child1_001, r2_child1, r2_child2], list(bcolls.all))
 
+    def test_bone_collection_bones(self):
+        # Build a hierarchy on the armature.
+        bcolls = self.arm.collections
+        bcoll_root = bcolls.new('root')
+        bcoll_child1 = bcolls.new('child1', parent=bcoll_root)
+        bcoll_child2 = bcolls.new('child2', parent=bcoll_root)
+
+        # Add bones to the armature & assign to collections.
+        bone_dict = self.add_bones(self.arm_ob)
+        bcoll_root.assign(bone_dict['root'])
+
+        bcoll_child1_bone_names = ('child_L', 'child_L_L', 'child_L_R')
+        for bone_name in bcoll_child1_bone_names:
+            bcoll_child1.assign(bone_dict[bone_name])
+
+        bcoll_child2_bone_names = ('child_R', 'child_R_L', 'child_R_R')
+        for bone_name in bcoll_child2_bone_names:
+            bcoll_child2.assign(bone_dict[bone_name])
+
+        # Check that the `.bones` property returns the expected ones.
+        self.assertEqual([self.arm.bones['root']], list(bcoll_root.bones))
+        self.assertEqual(set(bcoll_child1_bone_names), {b.name for b in bcoll_child1.bones})
+        self.assertEqual(set(bcoll_child2_bone_names), {b.name for b in bcoll_child2.bones})
+
     def test_bone_collection_armature_join(self):
         other_arm_ob, other_arm = self.create_armature()