Write first unit test

itchcraft/api.py

@@ -2,7 +2,7 @@
 
 from contextlib import ExitStack
 
-from .devices import find_devices
+from . import devices
 from .errors import CliError
 from .logging import get_logger
 
@@ -28,7 +28,7 @@ def start(self) -> None:  # pylint: disable=no-self-use
         with ExitStack() as stack:
             candidates = [
                 stack.enter_context(candidate)
-                for candidate in find_devices()
+                for candidate in devices.find_devices()
             ]
             if not candidates:
                 raise CliError('No bite healer connected')

itchcraft/backend.py

@@ -1,5 +1,7 @@
 """USB backend management"""
 
+from abc import ABC, abstractmethod
+from collections.abc import Callable
 import array
 from typing import Optional, Union, cast
 
@@ -8,7 +10,35 @@
 from .errors import BackendInitializationError, EndpointNotFound
 
 
-class UsbBulkTransferDevice:
+class BulkTransferDevice(ABC):
+    """Abstract base class for USB devices with two bulk transfer
+    endpoints."""
+
+    @abstractmethod
+    def bulk_transfer(
+        self,
+        request: Union[list[int], bytes, bytearray],
+    ) -> bytes:
+        """Sends a payload via USB bulk transfer and waits for a response
+        from the device.
+
+        :param `request`: the request payload from the host.
+
+        :return: the response received from the device.
+        """
+
+    @property
+    @abstractmethod
+    def product_name(self) -> Optional[str]:
+        """Product name of the device that this backend represents."""
+
+    @property
+    @abstractmethod
+    def serial_number(self) -> Optional[str]:
+        """Serial number of the device that this backend represents."""
+
+
+class UsbBulkTransferDevice(BulkTransferDevice):
     """USB device with two bulk transfer endpoints."""
 
     MAX_RESPONSE_LENGTH = 12
@@ -43,13 +73,6 @@ def bulk_transfer(
         self,
         request: Union[list[int], bytes, bytearray],
     ) -> bytes:
-        """Sends a payload via USB bulk transfer and waits for a response
-        from the device.
-
-        :param `request`: the request payload from the host.
-
-        :return: the response received from the device.
-        """
         response = array.array('B', bytearray(self.MAX_RESPONSE_LENGTH))
         assert self.device.write(self.endpoint_out, request) == len(
             request
@@ -59,16 +82,17 @@ def bulk_transfer(
 
     @property
     def product_name(self) -> Optional[str]:
-        """Product name of the device that this backend represents."""
-        return self.device.product
+        return cast(Optional[str], self.device.product)
 
     @property
     def serial_number(self) -> Optional[str]:
-        """Serial number of the device that this backend represents."""
-        return self.device.serial_number
+        return cast(Optional[str], self.device.serial_number)
 
 
-def _find_endpoint(interface, custom_match) -> usb.core.Endpoint:
+def _find_endpoint(
+    interface: usb.core.Interface,
+    custom_match: Callable[[usb.core.Endpoint], bool],
+) -> usb.core.Endpoint:
     if (
         endpoint := usb.util.find_descriptor(
             interface,

itchcraft/devices.py

@@ -1,22 +1,17 @@
 """Device management and discovery"""
 
-from collections.abc import Generator
-from contextlib import (
-    AbstractContextManager,
-    contextmanager,
-)
+from collections.abc import Iterator, Generator
+from contextlib import AbstractContextManager, contextmanager
 from typing import Any, cast
 
-import usb.core
+import usb.core  # type: ignore
 
 from .backend import UsbBulkTransferDevice
 from .heat_it import HeatItDevice
 from .device import Device
 
 
-def find_devices() -> (
-    Generator[AbstractContextManager[Device], None, None]
-):
+def find_devices() -> Iterator[AbstractContextManager[Device]]:
     """Finds the first available backend"""
     devices = cast(
         Generator[usb.core.Device, Any, None],
@@ -29,5 +24,5 @@ def find_devices() -> (
 @contextmanager
 def _heat_it_device(
     usb_device: usb.core.Device,
-) -> Generator[HeatItDevice, None, None]:
+) -> Iterator[HeatItDevice]:
     yield HeatItDevice(UsbBulkTransferDevice(usb_device))

itchcraft/heat_it.py

@@ -10,7 +10,7 @@
 )
 import usb.core  # type: ignore
 
-from .backend import UsbBulkTransferDevice
+from .backend import BulkTransferDevice
 from .device import Device
 from .logging import get_logger
 
@@ -23,9 +23,9 @@
 class HeatItDevice(Device):
     """A heat-it bite healer, configured over USB."""
 
-    device: UsbBulkTransferDevice
+    device: BulkTransferDevice
 
-    def __init__(self, device: UsbBulkTransferDevice) -> None:
+    def __init__(self, device: BulkTransferDevice) -> None:
         self.device = device
 
     def test_bootloader(self) -> bytes: