test: adding tests around adding components to Container ahead of refactoring.

Also relaxed the need to provide a parent to the constructor of Component.

Author: yt-ms

src/structurizr/model/component.py

@@ -82,7 +82,7 @@ class Component(StaticStructureElement):
     def __init__(
         self,
         *,
-        parent: "Container",
+        parent: "Container" = None,
         technology: str = "",
         code_elements: Iterable[CodeElement] = (),
         size: Optional[int] = None,

tests/unit/model/test_container.py

@@ -16,13 +16,19 @@
 
 import pytest
 
-from structurizr.model import Container, Model, SoftwareSystem
+from structurizr.model import Component, Container, Model, SoftwareSystem
 
 
 _model = Model()
 _system = _model.add_software_system(name="Sys")
 
 
+@pytest.fixture(scope="function")
+def empty_container() -> Container:
+    """Provide an empty Container on demand for test cases to use."""
+    return _system.add_container(name="Container", description="Description")
+
+
 @pytest.mark.parametrize(
     "attributes",
     [
@@ -35,3 +41,50 @@ def test_container_init(attributes):
     container = Container(**attributes)
     for attr, expected in attributes.items():
         assert getattr(container, attr) == expected
+
+
+def test_container_add_component_adds_to_component_list(empty_container: Container):
+    """Ensure that add_component() adds the new component to Container.components and sets up other properties."""
+    component = empty_container.add_component(name="Component")
+    assert component in empty_container.components
+    assert component.id != ""
+    assert component.model is _model
+    assert component.parent is empty_container
+
+
+@pytest.mark.xfail(strict=True)
+def test_container_add_constructed_component(empty_container: Container):
+    """Verify behaviour when adding a newly constructed Container rather than calling add_container()."""
+    component = Component(name="Component")
+    empty_container.add(component)
+    assert component in empty_container.components
+    assert component.id != ""  # Currently failing
+    assert component.model is _model  # Currently failing
+    assert component.parent is empty_container  # Currently failing
+
+
+def test_container_adding_component_twice_is_ok(empty_container: Container):
+    """Defensive check that adding the same component twice is OK."""
+    component = Component(name="Component")
+    empty_container.add(component)
+    empty_container.add(component)
+    assert len(empty_container.components) == 1
+
+
+@pytest.mark.xfail(strict=True)
+def test_container_adding_component_with_same_name_fails(empty_container: Container):
+    """Defensive check that adding a component with the same name as an existing one fails."""
+    empty_container.add_component(name="Component")
+    with pytest.raises(ValueError, match="Component with name .* already exists"):
+        empty_container.add_component(name="Component")
+    with pytest.raises(ValueError, match="Component with name .* already exists"):
+        empty_container.add(Component(name="Component"))  # Doesn't currently raise
+
+
+@pytest.mark.xfail(strict=True)
+def test_adding_component_with_existing_parent_fails(empty_container: Container):
+    """Defensive check that if a component already has a (different) parent then it can't be added."""
+    container2 = _system.add_container(name="Container 2", description="Description")
+    component = empty_container.add_component(name="Component")
+    with pytest.raises(ValueError):
+        container2.add(component)  # Doesn't currently raise