XCTest参数化测试重试时变量为nil的问题解决咨询

问题描述 #

我通过重写defaultTestSuite实现参数化UI测试，故意让值为2的用例失败。配置测试计划重试失败用例后，重试该用例时self.number变为nil，导致测试因空指针错误失败。如何避免这种情况？

原测试代码 #

import XCTest

final class HelloiOSUITests: XCTestCase {
    var number: Int?
    
    override func setUpWithError() throws {
        continueAfterFailure = false
    }

    func testExample() throws {
        guard let num = self.number else {
            XCTFail("Failed with NPE")
            throw NSError()
        }
        print("Running for number: \(num)")
        if num == 2 {
            XCTFail("Failing on purpose to demonstrate NPE issue.")
        }
    }
    
    override class var defaultTestSuite: XCTestSuite {
        get {
            let suite = XCTestSuite(name: NSStringFromClass(self))
            addTestCase(to: suite, value: 1)
            addTestCase(to: suite, value: 2)
            addTestCase(to: suite, value: 3)
            print("Test method count = \(suite.testCaseCount)")
            return suite
        }
    }
    
    static func addTestCase(to suite: XCTestSuite, value: Int) {
        for invocation in self.testInvocations {
            let testMethod = HelloiOSUITests(invocation: invocation)
            testMethod.number = value
            suite.addTest(testMethod)
        }
    }
}

问题原因 #

XCTest在重试失败用例时，会重新创建一个新的HelloiOSUITests实例，但这个新实例不会继承原实例的number属性值——原代码仅在初始创建测试实例时设置number，重试时新实例的number未被赋值，因此变为nil。

解决方法 #

将测试参数与NSInvocation绑定，利用其userInfo存储参数值，在测试实例的setUp阶段从invocation中取出参数并赋值给number。这样无论重试多少次，新实例都能从关联的invocation中获取正确参数。

修改后的代码 #

import XCTest

final class HelloiOSUITests: XCTestCase {
    var number: Int?
    
    override func setUpWithError() throws {
        continueAfterFailure = false
        // 从invocation的userInfo中取出参数赋值给number
        if let value = invocation.userInfo?["number"] as? Int {
            self.number = value
        }
    }

    func testExample() throws {
        guard let num = self.number else {
            XCTFail("Failed with NPE")
            throw NSError(domain: "HelloiOSUITests", code: -1)
        }
        print("Running for number: \(num)")
        if num == 2 {
            XCTFail("Failing on purpose to demonstrate NPE issue.")
        }
    }
    
    override class var defaultTestSuite: XCTestSuite {
        get {
            let suite = XCTestSuite(name: NSStringFromClass(self))
            addTestCase(to: suite, value: 1)
            addTestCase(to: suite, value: 2)
            addTestCase(to: suite, value: 3)
            print("Test method count = \(suite.testCaseCount)")
            return suite
        }
    }
    
    static func addTestCase(to suite: XCTestSuite, value: Int) {
        for invocation in self.testInvocations {
            // 复制invocation，避免修改原实例影响其他测试用例
            let copiedInvocation = invocation.copy() as! NSInvocation
            // 将参数存入invocation的userInfo
            copiedInvocation.userInfo = ["number": value]
            let testMethod = HelloiOSUITests(invocation: copiedInvocation)
            suite.addTest(testMethod)
        }
    }
}

关键修改点 #

• 在addTestCase中，复制原invocation并将参数存入其userInfo，避免修改原invocation导致参数污染
• 在setUpWithError中，从当前实例的invocation中取出userInfo里的参数，赋值给number
• 确保重试时新创建的测试实例能通过关联的invocation获取到正确的参数值

内容的提问来源于stack exchange，提问作者coldcake71