Use isNotFoundError which converts an error of the default type
`unknown` into NotFoundError if the error is an instance of NotFoundError.
Thrown errors are of type `unknown` by default so we should use methods
with type guards for better type narrowing.
Signed-off-by: Christina Ying Wang <christina@balena.io>
Tests using the mock `testWithData` method were not restoring the dockerode
prototype to the default values, making some tests behave differently
when run individually that when run with the suite.
This commit fixes the `testWithData` method and some malfunctioning v1
API tests because of the change. It doesn't fix all the tests
