diff --git a/src/blenderbim/blenderbim/bim/export_ifc.py b/src/blenderbim/blenderbim/bim/export_ifc.py
index 5a2113fa08..b27cc03f7c 100644
--- a/src/blenderbim/blenderbim/bim/export_ifc.py
+++ b/src/blenderbim/blenderbim/bim/export_ifc.py
@@ -114,7 +114,7 @@ class IfcExporter:
         IfcStore.edited_objs.clear()
 
     def sync_object_placement(self, obj):
-        blender_matrix = np.matrix(obj.matrix_world)
+        blender_matrix = np.array(obj.matrix_world)
         element = self.file.by_id(obj.BIMObjectProperties.ifc_definition_id)
         if not hasattr(element, "ObjectPlacement"):
             return
diff --git a/src/blenderbim/blenderbim/bim/module/root/operator.py b/src/blenderbim/blenderbim/bim/module/root/operator.py
index 544357b7c4..d230398dfa 100644
--- a/src/blenderbim/blenderbim/bim/module/root/operator.py
+++ b/src/blenderbim/blenderbim/bim/module/root/operator.py
@@ -117,11 +117,11 @@ class AssignClass(bpy.types.Operator):
     def _execute(self, context):
         objects = [bpy.data.objects.get(self.obj)] if self.obj else context.selected_objects
         self.file = IfcStore.get_file()
+        if not self.ifc_class:
+            self.ifc_class = context.scene.BIMRootProperties.ifc_class
         self.declaration = IfcStore.get_schema().declaration_by_name(self.ifc_class)
         if self.predefined_type == "USERDEFINED":
             self.predefined_type = self.userdefined_type
-        elif self.predefined_type == "":
-            predefined_type = None
         for obj in objects:
             self.assign_class(context, obj)
         return {"FINISHED"}
@@ -134,7 +134,7 @@ class AssignClass(bpy.types.Operator):
             self.file,
             **{
                 "ifc_class": self.ifc_class,
-                "predefined_type": self.predefined_type,
+                "predefined_type": self.predefined_type or None,
                 "name": obj.name,
             },
         )
diff --git a/src/blenderbim/test/bim/bootstrap.py b/src/blenderbim/test/bim/bootstrap.py
index 8f232ac681..a1f7897575 100644
--- a/src/blenderbim/test/bim/bootstrap.py
+++ b/src/blenderbim/test/bim/bootstrap.py
@@ -17,12 +17,109 @@
 # along with BlenderBIM Add-on.  If not, see <http://www.gnu.org/licenses/>.
 
 
+import re
 import bpy
 import pytest
 from blenderbim.bim.ifc import IfcStore
 
+
 class NewFile:
     @pytest.fixture(autouse=True)
     def setup(self):
         IfcStore.purge()
         bpy.ops.wm.read_homefile(app_template="")
+
+
+def scenario(function):
+    def subfunction(self):
+        run(function(self))
+
+    return subfunction
+
+
+def an_empty_ifc_project():
+    bpy.ops.bim.create_project()
+
+
+def i_add_a_cube():
+    bpy.ops.mesh.primitive_cube_add()
+
+
+def the_object_named_name_is_selected(name):
+    obj = bpy.context.scene.objects.get(name)
+    if not obj:
+        assert False, 'The object "{name}" could not be selected'
+    bpy.ops.object.select_all(action="DESELECT")
+    bpy.context.view_layer.objects.active = obj
+    obj.select_set(True)
+
+
+def i_select_value_in_prop(value, prop):
+    exec(f'bpy.context.{prop} = "{value}"')
+
+
+def i_press_operator(operator):
+    exec(f"bpy.ops.{operator}()")
+
+
+def the_object_named_name_exists(name):
+    obj = bpy.data.objects.get(name)
+    if not obj:
+        assert False, f'The object "{name}" does not exist'
+    return obj
+
+
+def an_ifc_file_exists():
+    ifc = IfcStore.get_file()
+    if not ifc:
+        assert False, "No IFC file is available"
+    return ifc
+
+
+def the_object_named_name_is_an_ifc_class(name, ifc_class):
+    ifc = an_ifc_file_exists()
+    element = ifc.by_id(the_object_named_name_exists(name).BIMObjectProperties.ifc_definition_id)
+    assert element.is_a(ifc_class), f'Object "{name}" is a {element.is_a()}'
+
+
+definitions = {
+    "an empty IFC project": an_empty_ifc_project,
+    "I add a cube": i_add_a_cube,
+    'the object named "(.*)" is selected': the_object_named_name_is_selected,
+    'I select "(.*)" in "(.*)"': i_select_value_in_prop,
+    'I press "(.*)"': i_press_operator,
+    'the object named "(.*)" is an "(.*)"': the_object_named_name_is_an_ifc_class,
+    "an IFC file exists": an_ifc_file_exists,
+}
+
+
+# Super lightweight Gherkin implementation
+def run(scenario):
+    for line in scenario.split("\n"):
+        line = line.strip()
+        if not line:
+            continue
+        match = None
+        for definition, callback in definitions.items():
+            match = re.search(definition, line)
+            if match:
+                try:
+                    callback(*match.groups())
+                except AssertionError as e:
+                    assert False, f"Failed: {line}, with error: {e}"
+                break
+        if not match:
+            assert False, f"Definition not implemented: {line}"
+    return True
+
+
+def run_debug(scenario, blend_filepath=None):
+    try:
+        result = run(scenario)
+    except Exception as e:
+        if blend_filepath:
+            bpy.ops.wm.save_as_mainfile(filepath=blend_filepath)
+        assert False, e
+    if blend_filepath:
+        bpy.ops.wm.save_as_mainfile(filepath=blend_filepath)
+    return result
diff --git a/src/blenderbim/test/bim/module/project/test_operator.py b/src/blenderbim/test/bim/module/project/test_operator.py
index a995246b90..5542f4ac7c 100644
--- a/src/blenderbim/test/bim/module/project/test_operator.py
+++ b/src/blenderbim/test/bim/module/project/test_operator.py
@@ -16,14 +16,17 @@
 # You should have received a copy of the GNU General Public License
 # along with BlenderBIM Add-on.  If not, see <http://www.gnu.org/licenses/>.
 
-import bpy
-import pytest
 import test.bim.bootstrap
-from blenderbim.bim.ifc import IfcStore
 
 
 class TestCreateProject(test.bim.bootstrap.NewFile):
+    @test.bim.bootstrap.scenario
     def test_creating_a_project(self):
-        assert IfcStore.get_file() is None
-        bpy.ops.bim.create_project()
-        assert IfcStore.get_file()
+        return """
+        When I press "bim.create_project"
+        Then an IFC file exists
+        And the object named "IfcProject/My Project" is an "IfcProject"
+        And the object named "IfcSite/My Site" is an "IfcSite"
+        And the object named "IfcBuilding/My Building" is an "IfcBuilding"
+        And the object named "IfcBuildingStorey/My Storey" is an "IfcBuildingStorey"
+        """
diff --git a/src/blenderbim/test/bim/module/root/__init__.py b/src/blenderbim/test/bim/module/root/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/src/blenderbim/test/bim/module/root/test_operator.py b/src/blenderbim/test/bim/module/root/test_operator.py
new file mode 100644
index 0000000000..7f395b2f0e
--- /dev/null
+++ b/src/blenderbim/test/bim/module/root/test_operator.py
@@ -0,0 +1,32 @@
+# BlenderBIM Add-on - OpenBIM Blender Add-on
+# Copyright (C) 2021 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of BlenderBIM Add-on.
+#
+# BlenderBIM Add-on 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 3 of the License, or
+# (at your option) any later version.
+#
+# BlenderBIM Add-on 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 BlenderBIM Add-on.  If not, see <http://www.gnu.org/licenses/>.
+
+import test.bim.bootstrap
+
+
+class TestCreateProject(test.bim.bootstrap.NewFile):
+    @test.bim.bootstrap.scenario
+    def test_assigning_a_class_to_a_cube(self):
+        return """
+        Given an empty IFC project
+        When I add a cube
+        And the object named "Cube" is selected
+        And I select "IfcWall" in "scene.BIMRootProperties.ifc_class"
+        And I press "bim.assign_class"
+        And the object named "IfcWall/Cube" is an "IfcWall"
+        """
diff --git a/src/blenderbim/test/bim/test_operator.py b/src/blenderbim/test/bim/test_operator.py
index 88446f10bf..608be4185d 100644
--- a/src/blenderbim/test/bim/test_operator.py
+++ b/src/blenderbim/test/bim/test_operator.py
@@ -17,7 +17,6 @@
 # along with BlenderBIM Add-on.  If not, see <http://www.gnu.org/licenses/>.
 
 import bpy
-import pytest
 import test.bim.bootstrap
 from blenderbim.bim.ifc import IfcStore