如何在 Swift 中对抛出函数进行单元测试? [英] How to unit test throwing functions in Swift?

问题描述

如何测试 Swift 2.0 中的函数是否抛出异常?如何断言正确的 ErrorType 被抛出?

How to test wether a function in Swift 2.0 throws or not? How to assert that the correct ErrorType is thrown?

推荐答案

更新了 Swift 4.1 的代码(在 Swift 5.2 中仍然有效)

Updated the code for Swift 4.1 (still valid with Swift 5.2)

这是使用 XCTAssertThrowsError 的 Fyodor Volchyok 的答案 的最新 Swift 版本:

Here's the latest Swift version of Fyodor Volchyok's answer who used XCTAssertThrowsError:

    enum MyError: Error {
        case someExpectedError
        case someUnexpectedError
    }

    func functionThatThrows() throws {
        throw MyError.someExpectedError
    }

    func testFunctionThatThrows() {
        XCTAssertThrowsError(try functionThatThrows()) { error in
            XCTAssertEqual(error as! MyError, MyError.someExpectedError)
        }
    }

如果你的 Error 枚举有关联的值，你可以让你的 Error 枚举符合 Equatable，或者使用 ifcase 语句:

If your Error enum has associated values, you can either have your Error enum conform to Equatable, or use the if case statement:

    enum MyError: Error, Equatable {
        case someExpectedError
        case someUnexpectedError
        case associatedValueError(value: Int)
    }

    func functionThatThrows() throws {
        throw MyError.associatedValueError(value: 10)
    }

    // Equatable pattern: simplest solution if you have a simple associated value that can be tested inside 1 XCTAssertEqual
    func testFunctionThatThrows() {
        XCTAssertThrowsError(try functionThatThrows()) { error in
            XCTAssertEqual(error as! MyError, MyError.associatedValueError(value: 10))
        }
    }

    // if case pattern: useful if you have one or more associated values more or less complex (struct, classes...)
    func testFunctionThatThrows() {
        XCTAssertThrowsError(try functionThatThrows()) { error in
            guard case MyError.associatedValueError(let value) = error else {
                return XCTFail()
            }

            XCTAssertEqual(value, 10)
            // if you have several values or if they require more complex tests, you can do it here
        }
    }

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