An idea...

[coretl]

In #641 we make connect in mock mode sync rather than async, but can't complete the job because Device.connect is async so child connects must also be async. This PR make connect return an optional Task which means we can make the mock path fully sync.

Too magic?

Also, tests need fixing...

[callumforrester]

Mocking is always magic anyway so the magic does not bother me

[DominicOram]

I feel like connect is a semi-user facing interface. For example, we use it quite a lot in dodal/mx_bluesky (which may be wrong I guess). This complicates the job for the caller quite a bit so I'm not a big fan. We could do something instead like:

class DeviceConnector:
    def connect_mock(self, device: Device, mock: LazyMock):
        # Connect serially, no errors to gather up as in mock mode
        for name, child_device in device.children():
            assert not child_device._mock_connect(mock=mock.child(name)) #Bit ugly this calls something private but I wouldn't want to confuse external callers of `Device`

class Device:
    ...

    def _mock_connect(self, mock):
        # Always connect in mock mode serially
        if isinstance(mock, LazyMock):
            # Use the provided mock
            self._mock = mock
        elif not self._mock:
            # Make one
            self._mock = LazyMock()
        self._connector.connect_mock(self, self._mock)

    async def connect(
        self,
        mock: bool | LazyMock = False,
        timeout: float = DEFAULT_TIMEOUT,
        force_reconnect: bool = False,
    ) -> None:
        """Connect self and all child Devices.

        Contains a timeout that gets propagated to child.connect methods.

        Parameters
        ----------
        mock:
            If True then use ``MockSignalBackend`` for all Signals
        timeout:
            Time to wait before failing with a TimeoutError.
        """
        if mock:
            self._mock_connect(mock)
        else:
            ...

[coretl]

I think the gains are marginal, so let's abandon this idea