feat!: add Scenario classes that match the ops status classes (#142)

Adds classes that match the ops status classes:

* UnknownStatus
* ActiveStatus
* WaitingStatus
* MaintenanceStatus
* BlockedStatus
* ErrorStatus

README.md

@@ -85,9 +85,12 @@ With that, we can write the simplest possible scenario test:
 def test_scenario_base():
     ctx = scenario.Context(MyCharm, meta={"name": "foo"})
     out = ctx.run(ctx.on.start(), scenario.State())
-    assert out.unit_status == ops.UnknownStatus()
+    assert out.unit_status == scenario.UnknownStatus()
 ```
 
+Note that you should always compare the app and unit status using `==`, not `is`. You can compare
+them to either the `scenario` objects, or the `ops` ones.
+
 Now let's start making it more complicated. Our charm sets a special state if it has leadership on 'start':
 
 ```python
@@ -110,7 +113,7 @@ class MyCharm(ops.CharmBase):
 def test_status_leader(leader):
     ctx = scenario.Context(MyCharm, meta={"name": "foo"})
     out = ctx.run(ctx.on.start(), scenario.State(leader=leader))
-    assert out.unit_status == ops.ActiveStatus('I rule' if leader else 'I am ruled')
+    assert out.unit_status == scenario.ActiveStatus('I rule' if leader else 'I am ruled')
 ```
 
 By defining the right state we can programmatically define what answers will the charm get to all the questions it can
@@ -165,15 +168,15 @@ def test_statuses():
     ctx = scenario.Context(MyCharm, meta={"name": "foo"})
     out = ctx.run(ctx.on.start(), scenario.State(leader=False))
     assert ctx.unit_status_history == [
-        ops.UnknownStatus(),
-        ops.MaintenanceStatus('determining who the ruler is...'),
-        ops.WaitingStatus('checking this is right...'),
+        scenario.UnknownStatus(),
+        scenario.MaintenanceStatus('determining who the ruler is...'),
+        scenario.WaitingStatus('checking this is right...'),
     ]
-    assert out.unit_status == ops.ActiveStatus("I am ruled")
+    assert out.unit_status == scenario.ActiveStatus("I am ruled")
 
     # similarly you can check the app status history:
     assert ctx.app_status_history == [
-        ops.UnknownStatus(),
+        scenario.UnknownStatus(),
         ...
     ]
 ```
@@ -198,9 +201,9 @@ class MyCharm(ops.CharmBase):
 
 # ...
 ctx = scenario.Context(MyCharm, meta={"name": "foo"})
-ctx.run(ctx.on.start(), scenario.State(unit_status=ops.ActiveStatus('foo')))
+ctx.run(ctx.on.start(), scenario.State(unit_status=scenario.ActiveStatus('foo')))
 assert ctx.unit_status_history == [
-    ops.ActiveStatus('foo'),  # now the first status is active: 'foo'!
+    scenario.ActiveStatus('foo'),  # now the first status is active: 'foo'!
     # ...
 ]
 ```
@@ -248,7 +251,7 @@ def test_emitted_full():
         capture_deferred_events=True,
         capture_framework_events=True,
     )
-    ctx.run(ctx.on.start(), scenario.State(deferred=[scenario.Event("update-status").deferred(MyCharm._foo)]))
+    ctx.run(ctx.on.start(), scenario.State(deferred=[ctx.on.update_status().deferred(MyCharm._foo)]))
 
     assert len(ctx.emitted_events) == 5
     assert [e.handle.kind for e in ctx.emitted_events] == [
@@ -396,8 +399,6 @@ meta = {
 }
 ctx = scenario.Context(ops.CharmBase, meta=meta, unit_id=1)
 ctx.run(ctx.on.start(), state_in)  # invalid: this unit's id cannot be the ID of a peer.
-
-
 ```
 
 ### SubordinateRelation

scenario/__init__.py

@@ -4,14 +4,18 @@
 from scenario.context import ActionOutput, Context
 from scenario.state import (
     Action,
+    ActiveStatus,
     Address,
     BindAddress,
+    BlockedStatus,
     CloudCredential,
     CloudSpec,
     Container,
     DeferredEvent,
+    ErrorStatus,
     ExecOutput,
     ICMPPort,
+    MaintenanceStatus,
     Model,
     Mount,
     Network,
@@ -27,6 +31,8 @@
     SubordinateRelation,
     TCPPort,
     UDPPort,
+    UnknownStatus,
+    WaitingStatus,
     deferred,
 )
 
@@ -58,4 +64,10 @@
     "StoredState",
     "State",
     "DeferredEvent",
+    "ErrorStatus",
+    "BlockedStatus",
+    "WaitingStatus",
+    "MaintenanceStatus",
+    "ActiveStatus",
+    "UnknownStatus",
 ]

scenario/context.py

@@ -557,9 +557,9 @@ def _get_storage_root(self, name: str, index: int) -> Path:
     def _record_status(self, state: "State", is_app: bool):
         """Record the previous status before a status change."""
         if is_app:
-            self.app_status_history.append(cast("_EntityStatus", state.app_status))
+            self.app_status_history.append(state.app_status)
         else:
-            self.unit_status_history.append(cast("_EntityStatus", state.unit_status))
+            self.unit_status_history.append(state.unit_status)
 
     def manager(self, event: "_Event", state: "State"):
         """Context manager to introspect live charm object before and after the event is emitted.

scenario/mocking.py

@@ -43,6 +43,7 @@
     Network,
     PeerRelation,
     Storage,
+    _EntityStatus,
     _port_cls_by_protocol,
     _RawPortProtocolLiteral,
     _RawStatusLiteral,
@@ -338,7 +339,8 @@ def status_set(
         is_app: bool = False,
     ):
         self._context._record_status(self._state, is_app)
-        self._state._update_status(status, message, is_app)
+        status_obj = _EntityStatus.from_status_name(status, message)
+        self._state._update_status(status_obj, is_app)
 
     def juju_log(self, level: str, message: str):
         self._context.juju_log.append(JujuLogLine(level, message))

scenario/state.py

@@ -16,6 +16,7 @@
     TYPE_CHECKING,
     Any,
     Callable,
+    ClassVar,
     Dict,
     Final,
     FrozenSet,
@@ -32,6 +33,7 @@
 )
 from uuid import uuid4
 
+import ops
 import yaml
 from ops import pebble
 from ops.charm import CharmBase, CharmEvents
@@ -956,18 +958,17 @@ def get_notice(
 class _EntityStatus:
     """This class represents StatusBase and should not be interacted with directly."""
 
-    # Why not use StatusBase directly? Because that's not json-serializable.
+    # Why not use StatusBase directly? Because that can't be used with
+    # dataclasses.asdict to then be JSON-serializable.
 
     name: _RawStatusLiteral
     message: str = ""
 
+    _entity_statuses: ClassVar[Dict[str, Type["_EntityStatus"]]] = {}
+
     def __eq__(self, other):
         if isinstance(other, (StatusBase, _EntityStatus)):
             return (self.name, self.message) == (other.name, other.message)
-        logger.warning(
-            f"Comparing Status with {other} is not stable and will be forbidden soon."
-            f"Please compare with StatusBase directly.",
-        )
         return super().__eq__(other)
 
     def __repr__(self):
@@ -976,17 +977,89 @@ def __repr__(self):
             return f"{status_type_name}()"
         return f"{status_type_name}('{self.message}')"
 
+    @classmethod
+    def from_status_name(
+        cls,
+        name: _RawStatusLiteral,
+        message: str = "",
+    ) -> "_EntityStatus":
+        # Note that this won't work for UnknownStatus.
+        # All subclasses have a default 'name' attribute, but the type checker can't tell that.
+        return cls._entity_statuses[name](message=message)  # type:ignore
+
+    @classmethod
+    def from_ops(cls, obj: StatusBase) -> "_EntityStatus":
+        return cls.from_status_name(cast(_RawStatusLiteral, obj.name), obj.message)
+
+
+@dataclasses.dataclass(frozen=True, eq=False, repr=False)
+class UnknownStatus(_EntityStatus, ops.UnknownStatus):
+    __doc__ = ops.UnknownStatus.__doc__
+
+    name: Literal["unknown"] = "unknown"
+
+    def __init__(self):
+        super().__init__(name=self.name)
+
+
+@dataclasses.dataclass(frozen=True, eq=False, repr=False)
+class ErrorStatus(_EntityStatus, ops.ErrorStatus):
+    __doc__ = ops.ErrorStatus.__doc__
+
+    name: Literal["error"] = "error"
+
+    def __init__(self, message: str = ""):
+        super().__init__(name="error", message=message)
+
+
+@dataclasses.dataclass(frozen=True, eq=False, repr=False)
+class ActiveStatus(_EntityStatus, ops.ActiveStatus):
+    __doc__ = ops.ActiveStatus.__doc__
+
+    name: Literal["active"] = "active"
+
+    def __init__(self, message: str = ""):
+        super().__init__(name="active", message=message)
 
-def _status_to_entitystatus(obj: StatusBase) -> _EntityStatus:
-    """Convert StatusBase to _EntityStatus."""
-    statusbase_subclass = type(StatusBase.from_name(obj.name, obj.message))
 
-    class _MyClass(_EntityStatus, statusbase_subclass):
-        # Custom type inheriting from a specific StatusBase subclass to support instance checks:
-        #  isinstance(state.unit_status, ops.ActiveStatus)
-        pass
+@dataclasses.dataclass(frozen=True, eq=False, repr=False)
+class BlockedStatus(_EntityStatus, ops.BlockedStatus):
+    __doc__ = ops.BlockedStatus.__doc__
 
-    return _MyClass(cast(_RawStatusLiteral, obj.name), obj.message)
+    name: Literal["blocked"] = "blocked"
+
+    def __init__(self, message: str = ""):
+        super().__init__(name="blocked", message=message)
+
+
+@dataclasses.dataclass(frozen=True, eq=False, repr=False)
+class MaintenanceStatus(_EntityStatus, ops.MaintenanceStatus):
+    __doc__ = ops.MaintenanceStatus.__doc__
+
+    name: Literal["maintenance"] = "maintenance"
+
+    def __init__(self, message: str = ""):
+        super().__init__(name="maintenance", message=message)
+
+
+@dataclasses.dataclass(frozen=True, eq=False, repr=False)
+class WaitingStatus(_EntityStatus, ops.WaitingStatus):
+    __doc__ = ops.WaitingStatus.__doc__
+
+    name: Literal["waiting"] = "waiting"
+
+    def __init__(self, message: str = ""):
+        super().__init__(name="waiting", message=message)
+
+
+_EntityStatus._entity_statuses.update(
+    unknown=UnknownStatus,
+    error=ErrorStatus,
+    active=ActiveStatus,
+    blocked=BlockedStatus,
+    maintenance=MaintenanceStatus,
+    waiting=WaitingStatus,
+)
 
 
 @dataclasses.dataclass(frozen=True)
@@ -1033,6 +1106,11 @@ def __post_init__(self):
                 "please use TCPPort, UDPPort, or ICMPPort",
             )
 
+    def __eq__(self, other: object) -> bool:
+        if isinstance(other, (_Port, ops.Port)):
+            return (self.protocol, self.port) == (other.protocol, other.port)
+        return False
+
 
 @dataclasses.dataclass(frozen=True)
 class TCPPort(_Port):
@@ -1112,6 +1190,11 @@ class Storage(_max_posargs(1)):
     index: int = dataclasses.field(default_factory=next_storage_index)
     # Every new Storage instance gets a new one, if there's trouble, override.
 
+    def __eq__(self, other: object) -> bool:
+        if isinstance(other, (Storage, ops.Storage)):
+            return (self.name, self.index) == (other.name, other.index)
+        return False
+
     def get_filesystem(self, ctx: "Context") -> Path:
         """Simulated filesystem root in this context."""
         return ctx._get_storage_root(self.name, self.index)
@@ -1182,23 +1265,45 @@ class State(_max_posargs(0)):
     )
     """Contents of a charm's stored state."""
 
-    # the current statuses. Will be cast to _EntitiyStatus in __post_init__
-    app_status: Union[StatusBase, _EntityStatus] = _EntityStatus("unknown")
+    # the current statuses.
+    app_status: _EntityStatus = UnknownStatus()
     """Status of the application."""
-    unit_status: Union[StatusBase, _EntityStatus] = _EntityStatus("unknown")
+    unit_status: _EntityStatus = UnknownStatus()
     """Status of the unit."""
     workload_version: str = ""
     """Workload version."""
 
     def __post_init__(self):
+        # Let people pass in the ops classes, and convert them to the appropriate Scenario classes.
         for name in ["app_status", "unit_status"]:
             val = getattr(self, name)
             if isinstance(val, _EntityStatus):
                 pass
             elif isinstance(val, StatusBase):
-                object.__setattr__(self, name, _status_to_entitystatus(val))
+                object.__setattr__(self, name, _EntityStatus.from_ops(val))
             else:
                 raise TypeError(f"Invalid status.{name}: {val!r}")
+        normalised_ports = [
+            _Port(protocol=port.protocol, port=port.port)
+            if isinstance(port, ops.Port)
+            else port
+            for port in self.opened_ports
+        ]
+        if self.opened_ports != normalised_ports:
+            object.__setattr__(self, "opened_ports", normalised_ports)
+        normalised_storage = [
+            Storage(name=storage.name, index=storage.index)
+            if isinstance(storage, ops.Storage)
+            else storage
+            for storage in self.storages
+        ]
+        if self.storages != normalised_storage:
+            object.__setattr__(self, "storages", normalised_storage)
+        # ops.Container, ops.Model, ops.Relation, ops.Secret should not be instantiated by charmers.
+        # ops.Network does not have the relation name, so cannot be converted.
+        # ops.Resources does not contain the source of the resource, so cannot be converted.
+        # ops.StoredState is not convenient to initialise with data, so not useful here.
+
         # It's convenient to pass a set, but we really want the attributes to be
         # frozen sets to increase the immutability of State objects.
         for name in [
@@ -1228,14 +1333,13 @@ def _update_workload_version(self, new_workload_version: str):
 
     def _update_status(
         self,
-        new_status: _RawStatusLiteral,
-        new_message: str = "",
+        new_status: _EntityStatus,
         is_app: bool = False,
     ):
-        """Update the current app/unit status and add the previous one to the history."""
+        """Update the current app/unit status."""
         name = "app_status" if is_app else "unit_status"
         # bypass frozen dataclass
-        object.__setattr__(self, name, _EntityStatus(new_status, new_message))
+        object.__setattr__(self, name, new_status)
 
     def _update_opened_ports(self, new_ports: FrozenSet[_Port]):
         """Update the current opened ports."""
@@ -1262,10 +1366,7 @@ def with_leadership(self, leader: bool) -> "State":
     def with_unit_status(self, status: StatusBase) -> "State":
         return dataclasses.replace(
             self,
-            status=dataclasses.replace(
-                cast(_EntityStatus, self.unit_status),
-                unit=_status_to_entitystatus(status),
-            ),
+            unit_status=_EntityStatus.from_ops(status),
         )
 
     def get_container(self, container: str, /) -> Container:

tests/test_e2e/test_actions.py

@@ -5,7 +5,7 @@
 
 from scenario import Context
 from scenario.context import InvalidEventError
-from scenario.state import Action, State, _Event, next_action_id
+from scenario.state import Action, State, next_action_id
 
 
 @pytest.fixture(scope="function")