Quick&dirty Nimble matcher for testing ErrorType equality. Requires no casting or Equatable conformance!

MatchError.swift

@testable import Nimble

public func matchError<T: ErrorType>(expectedValue: T?) -> NonNilMatcherFunc<ErrorType> {
    return NonNilMatcherFunc { actualExpression, failureMessage in
        defer { failureMessage.postfixMessage = "match <\(T.self).\(stringify(expectedValue))>" }

        if try actualExpression.evaluate() is T {
            return try equal(expectedValue as? NSError).matches(
                actualExpression.cast({ $0 as? NSError }),
                failureMessage: failureMessage
            )
        }

        return false
    }
}

//////

enum Error: ErrorType {
    case MyError
    case OtherError
}

enum AnotherError: ErrorType {
    case Foo
}

let errType: ErrorType = Error.MyError

expect(errType).to(matchError(Error.MyError))
expect(errType).to(matchError(Error.OtherError))
expect(errType).to(matchError(AnotherError.Foo))