使您的DBError符合Equatable：

enum DBError: ErrorType, Equatable {
  case CannotBeEmpty(message: String)
}

func ==(lhs: DBError, rhs: DBError) -> Bool {
  switch (lhs, rhs) {
    case (.CannotBeEmpty(let leftMessage), .CannotBeEmpty(let rightMessage)):
      return leftMessage == rightMessage
  }
}

然后，您可以在XCTAssertEqual中使用它：

func testExample() {
  do {
    try isValid()
  }
  catch let e as DBError {
    XCTAssertEqual(e, DBError.CannotBeEmpty(message: "Street"))
  }
  catch {
    XCTFail("Wrong error")
  }
}

或者创建您自己的XCTAssertThrows。

enum DBError: ErrorType, Equatable {
  case CannotBeEmpty(message: String)
}

func ==(lhs: DBError, rhs: DBError) -> Bool {
  switch (lhs, rhs) {
    case (.CannotBeEmpty(let leftMessage), .CannotBeEmpty(let rightMessage)):
      return leftMessage == rightMessage
  }
}

还有：

func XCTAssertThrows<T: ErrorType where T: Equatable>(error: T, block: () throws -> ()) {
  do {
    try block()
  }
  catch let e as T {
    XCTAssertEqual(e, error)
  }
  catch {
    XCTFail("Wrong error")
  }
}

class TestsTests: XCTestCase {

    func testExample() {
      XCTAssertThrows(DBError.CannotBeEmpty(message: "Street")) { try isValid() }
    }

}

或者，只需使用可选的try：

extension XCTestCase {
    func XCTAssertThrows(@autoclosure expression: () throws -> Void, _ message: String = "", file: String = __FILE__, line: UInt = __LINE__) {
        XCTAssert((try? expression()) == nil, message, file: file, line: line)
    }
}

无需符合Equatable

到目前为止，我找到的最佳解决方案是：

do {
    try searchOptionsManager.isValidForMode(.Address)
    XCTAssertTrue(false)
} catch {
    XCTAssertTrue(true)
}

通过这种方式，您可以测试是否真的引发了异常，但无法检查引发了什么类型的异常。

以下是@robertvojta的回答，针对Xcode 9和Swift 3 - 4进行了一些修改：

extension XCTestCase {
    func XCTAssertThrows<ErrorType: Error, T>(expression: @autoclosure () throws -> T, error: ErrorType) where ErrorType: Equatable {
        do {
            _ = try expression()
        } catch let caughtError as ErrorType {
            XCTAssertEqual(caughtError, error)
        } catch {
            XCTFail("Wrong error")
        }
    }
}

用法：

enum APIError: LocalizedError {
    case cancelled

    public var errorDescription: String? {
        switch self {
        case .cancelled:
            return "The operation has been cancelled by user."
        }
    }
}

func testThatIsThrowsCancelledByUserError() {
    XCTAssertThrows(expression: try api.cancelLoginOperation(), error: APIError.cancelled)
}

如果您知道函数会抛出错误，那么您还应该确保在未抛出错误的情况下失败。
我在这里修改了来自@robertvojta和@vadim-bulavin的回答：

extension XCTestCase {
    func XCTAssertThrows<ErrorType: Error, T>(expression: @autoclosure () throws -> T, error: ErrorType) where ErrorType: Equatable {
        do {
            _ = try expression()
            XCTFail("No error thrown")
        } catch let caughtError as ErrorType {
            XCTAssertEqual(caughtError, error)
        } catch {
            XCTFail("Wrong error")
        }
    }
}

用法：

enum APIError: LocalizedError {
    case cancelled

    public var errorDescription: String? {
        switch self {
        case .cancelled:
            return "The operation has been cancelled by user."
        }
    }
}

func testThatIsThrowsCancelledByUserError() {
    XCTAssertThrows(expression: try api.cancelLoginOperation(), error: APIError.cancelled)
}

下面是一个示例，您将了解try-catch检查下面的代码

func validateCredencials() throws {

guard username.characters.count > 0  && password.characters.count > 0 
else { throw EncryptionType.Empty }
    guard password.characters.count >= 5 else { throw EncryptionType.Short }
}
    do {
    try validateCredencials()
    }catch EncryptionType.Empty {
        print("password Empty")

    } catch EncryptionType.Short {
        print("Password too shoot")
    }catch {
        print("Some thing went Wrong")
    }

希望你能理解