Modifiers: Armature deformation test for various modifier settings

Test for armature deform modifier settings that are not yet covered by other tests:

- Vertex Group vs. Envelope deformation and both combined.
- Vertex group masking ('vertex_group' setting of the modifier)
- Inverted vertex group masking
- Preserve Volume (dual quaternions)
- Vertex Group/Envelope influence mixing (bone option)
- B-Bone deformation
- Multi-modifier mixing

Each case has a new test/expected mesh pair in the modifiers test.

Pull Request: https://projects.blender.org/blender/blender/pulls/141054

tests/python/modules/mesh_test.py

@@ -61,6 +61,23 @@ class ModifierSpec:
                " with parameters: " + str(self.modifier_parameters)
 
 
+class MultiModifierSpec:
+    """
+    Holds a list of Deform modifiers that must be applied together to yield the expected result.
+    """
+
+    def __init__(self, modifiers):
+        """
+        Constructs a multi-modifier spec.
+
+        :arg modifiers - list of modifier specs
+        """
+        self.modifiers = modifiers
+
+    def __str__(self):
+        return "Multi-Modifier: [" + ', '.join(str(modspec) for modspec in self.modifiers) + "]"
+
+
 class ParticleSystemSpec:
     """
     Holds a Particle System modifier and its parameters.
@@ -491,6 +508,13 @@ class SpecMeshTest(MeshTest):
                     self._apply_modifier(
                         evaluated_test_object, operation.modifier_name)
 
+            elif isinstance(operation, MultiModifierSpec):
+                for modspec in operation.modifiers:
+                    self._add_modifier(evaluated_test_object, modspec)
+                if self.apply_modifier:
+                    self._apply_all_modifiers(
+                        evaluated_test_object)
+
             elif isinstance(operation, OperatorSpecEditMode):
                 self._apply_operator_edit_mode(
                     evaluated_test_object, operation)
@@ -598,6 +622,12 @@ class SpecMeshTest(MeshTest):
         else:
             raise Exception("This object type is not yet supported!")
 
+    def _apply_all_modifiers(self, test_object):
+        if test_object.type in ['CURVE', 'MESH']:
+            bpy.ops.object.convert(target='MESH')
+        else:
+            raise Exception("This object type is not yet supported!")
+
     def _bake_current_simulation(self, test_object, test_modifier_name, frame_end):
         """
         FLUID: Bakes the simulation