pytest-selfie: `FS.assertFailed`

[nedtwigg]

This is FSJava as supplied by the junit5 runner

https://github.com/diffplug/selfie-python-wip/blob/e6c59053316e3492b3552a5dcf54c9ba598ee7e3/jvm/selfie-runner-junit5/src/main/kotlin/com/diffplug/selfie/junit5/SnapshotSystemJUnit5.kt#L57-L59

And this is FSOkio as supplied by the kotest runner

https://github.com/diffplug/selfie-python-wip/blob/e6c59053316e3492b3552a5dcf54c9ba598ee7e3/jvm/selfie-runner-kotest/src/commonMain/kotlin/com/diffplug/selfie/kotest/FSOkio.kt#L44-L63

The key thing to note here is that the exception has two cases:

• expected and actual both null -> can be a regular AssertionError
• should be an equals assertion:
  • unittest -> self.assertEqual(expected, actual, msg)
  • pytest -> assert expected == actual, msg

[nedtwigg]

@Trickybrain this would be a good thing to work on too, we will need it soon

[nedtwigg]

@Trickybrain we still need this. It should go here:

selfie/python/pytest-selfie/pytest_selfie/plugin.py

Lines 22 to 33 in 7b31cc6

	class FSImplementation(FS):
	def file_walk(self, typed_path, walk):
	pass
	def file_read_binary(self, typed_path) -> bytes:
	return b""
	def file_write_binary(self, typed_path, content: bytes):
	pass
	def assert_failed(self, message: str, expected=None, actual=None) -> Exception:
	raise Exception(message)

Might as well implement the other methods in FSImplementation while you're there.