Implement basic Gherkin-based QA system

src/ifcblenderexport/features/steps/example_steps.py

@@ -0,0 +1,14 @@
+import ifcopenshell
+from behave import given, when, then, step
+
+@given('the IFC file "{file}"')
+def step_impl(context, file):
+    context.file = ifcopenshell.open(file)
+
+@then('the element {id} is an {ifc_class}')
+def step_impl(context, id, ifc_class):
+    assert context.file.by_id(id).is_a(ifc_class)
+
+@then('the element {id} should not exist because {reason}')
+def step_impl(context, id, reason):
+    assert not context.file.by_id(id)