test: add tests around adding containers to systems ahead of some refactoring.

Author: yt-ms

src/structurizr/model/container.py

@@ -79,7 +79,7 @@ class Container(StaticStructureElement):
     def __init__(
         self,
         *,
-        parent: "SoftwareSystem",
+        parent: "SoftwareSystem" = None,
         technology: str = "",
         components: Iterable[Component] = (),
         **kwargs,

tests/unit/model/test_software_system.py

@@ -19,6 +19,7 @@
 import pytest
 
 from structurizr.model.model import Model
+from structurizr.model.container import Container
 from structurizr.model.software_system import SoftwareSystem
 
 
@@ -28,6 +29,12 @@ def empty_model() -> Model:
     return Model()
 
 
+@pytest.fixture(scope="function")
+def empty_system() -> SoftwareSystem:
+    """Provide an empty SoftwareSystem on demand for test cases to use."""
+    return Model().add_software_system("Sys")
+
+
 @pytest.mark.parametrize(
     "attributes",
     [
@@ -55,3 +62,52 @@ def test_add_container_technology_is_optional(empty_model: Model):
     system = empty_model.add_software_system(name="sys")
     container = system.add_container(name="Container", description="Description")
     assert container.technology == ""
+
+    
+@pytest.mark.xfail(strict=True)
+def test_software_system_add_container_adds_to_container_list(empty_system: SoftwareSystem):
+    """Ensure that add_container() adds the new container to SoftwareSystem.containers and sets up other properties."""
+    container = empty_system.add_container(name="Container", description="Description")
+    assert container in empty_system.containers
+    assert container.id != ""
+    assert container.model is empty_system.model
+    assert container.parent is empty_system
+
+
+@pytest.mark.xfail(strict=True)
+def test_software_system_add_constructed_container(empty_system: SoftwareSystem):
+    """Verify behaviour when adding a newly constructed Container rather than calling add_container()."""
+    container = Container(name="Container")
+    empty_system += container
+    assert container in empty_system.containers
+    assert container.id != ""
+    assert container.model is empty_system.model
+    assert container.parent is empty_system
+
+
+@pytest.mark.xfail(strict=True)
+def test_software_system_adding_container_twice_is_ok(empty_system: SoftwareSystem):
+    """Defensive check that adding the same container twice is OK."""
+    container = Container(name="Container")
+    empty_system += container
+    empty_system += container
+    assert len(empty_system.containers) == 1
+
+
+@pytest.mark.xfail(strict=True)
+def test_software_system_adding_container_with_same_name_fails(empty_system: SoftwareSystem):
+    """Defensive check that adding a container with the same name as an existing one fails."""
+    empty_system.add_container(name="Container")
+    with pytest.raises(ValueError, match="Container with name .* already exists"):
+        empty_system.add_container(name="Container")
+    with pytest.raises(ValueError, match="Container with name .* already exists"):
+        empty_system += Container(name="Container")
+
+
+@pytest.mark.xfail(strict=True)
+def test_software_system_adding_container_with_existing_parent_fails(empty_system: SoftwareSystem):
+    """Defensive check that if a container already has a (different) parent then it can't be added."""
+    system2 = empty_system.model.add_software_system(name="System 2", description="Description")
+    container = empty_system.add_container(name="Container")
+    with pytest.raises(ValueError, match="Container with name .* already has parent"):
+        system2 += container