如何动态添加 XCTestCase

Question

我正在为一个白标项目编写 UI 测试，其中每个应用程序都有一组不同的菜单项。测试点击每个菜单项并截取屏幕截图（使用 fastlane snapshot）。

目前这一切都发生在一个名为 testScreenshotAllMenuItems() 的 XCTestCase 中，它看起来像这样：

func testScreenshotAllMenuItems() {
    // Take a screenshot of the menu
    openTheMenu()
    snapshot("Menu")
    var cells:[XCUIElement] = []

    // Store each menu item for use later
    for i in 0..<app.tables.cells.count {
        cells.append(app.tables.cells.element(boundBy: i))
    }

    // Loop through each menu item
    for menuItem in cells.enumerated() {
        let exists = menuItem.element.waitForExistence(timeout: 5)
        if exists && menuItem.element.isHittable {
            // Only tap on the menu item if it isn't an external link
            let externalLink = menuItem.element.children(matching: .image)["external link"]
            if !externalLink.exists {
                var name = "\(menuItem.offset)"
                let cellText = menuItem.element.children(matching: .staticText).firstMatch
                if cellText.label != "" {
                    name += "-\(cellText.label.replacingOccurrences(of: " ", with: "-"))"
                }
                print("opening \(name)")
                menuItem.element.tap()
                // Screenshot this view and then re-open the menu
                snapshot(name)
                openTheMenu()
            }
        }
    }
}

我希望能够动态生成每个屏幕截图，因为它是自己的测试用例，以便将这些屏幕截图正确地报告为单独的测试，可能类似于：

[T] Screenshots
    [t] testFavouritesViewScreenShot()        ✓
    [t] testGiveFeedbackViewScreenShot()      ✓
    [t] testSettingsViewScreenShot()          ✓

我看过 creating tests programmatically 上的文档，但我不确定如何快速设置它。 - 理想情况下，我会使用闭包将现有的屏幕截图测试包装到它们自己的 XCTestCase - 我想象如下，但似乎没有任何有用的初始化方法来实现这一点：

for menuItem in cells {
    let test = XCTestCase(closure: {
        menuItem.tap()
        snapshot("menuItemName")
    })
    test.run()
}

我不明白文档建议使用的调用和选择器的组合，我找不到任何好的例子，请给我指明正确的方向，或者分享你的任何例子。

Answer 1

您可能无法在纯 swift 中执行此操作，因为 NSInvocation 不再是 swift api 的一部分。

XCTest 依靠 + (NSArray<NSInvocation *> *)testInvocations 函数获取一个 XCTestCase class 中的测试方法列表。您可以假设的默认实现只是找到所有以 test 前缀和 return 开头的方法，它们包含在 NSInvocation 中。（您可以阅读更多关于 NSInvocation here）
因此，如果我们想在运行时声明测试，这就是我们感兴趣的地方。
不幸的是 NSInvocation 不再是 swift api 的一部分，我们无法覆盖此方法。

如果您可以使用一点点 ObjC，那么我们可以创建超级 class，它在内部隐藏 NSInvocation 详细信息，并为子 class 提供 swift-友好 api es。

/// Parent.h

/// SEL is just pointer on C struct so we cannot put it inside of NSArray.  
/// Instead we use this class as wrapper.
@interface _QuickSelectorWrapper : NSObject
- (instancetype)initWithSelector:(SEL)selector;
@end

@interface ParametrizedTestCase : XCTestCase
/// List of test methods to call. By default return nothing
+ (NSArray<_QuickSelectorWrapper *> *)_qck_testMethodSelectors;
@end

/// Parent.m

#include "Parent.h"
@interface _QuickSelectorWrapper ()
@property(nonatomic, assign) SEL selector;
@end

@implementation _QuickSelectorWrapper
- (instancetype)initWithSelector:(SEL)selector {
    self = [super init];
    _selector = selector;
    return self;
}
@end

@implementation ParametrizedTestCase
+ (NSArray<NSInvocation *> *)testInvocations {
    // here we take list of test selectors from subclass
    NSArray<_QuickSelectorWrapper *> *wrappers = [self _qck_testMethodSelectors];
    NSMutableArray<NSInvocation *> *invocations = [NSMutableArray arrayWithCapacity:wrappers.count];

    // And wrap them in NSInvocation as XCTest api require
    for (_QuickSelectorWrapper *wrapper in wrappers) {
        SEL selector = wrapper.selector;
        NSMethodSignature *signature = [self instanceMethodSignatureForSelector:selector];
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
        invocation.selector = selector;

        [invocations addObject:invocation];
    }

    /// If you want to mix parametrized test with normal `test_something` then you need to call super and append his invocations as well.
    /// Otherwise `test`-prefixed methods will be ignored
    return invocations;
}

+ (NSArray<_QuickSelectorWrapper *> *)_qck_testMethodSelectors {
    return @[];
}
@end

所以现在我们的 swift 测试 classes 需要继承这个 class 并覆盖 _qck_testMethodSelectors:

/// RuntimeTests.swift

class RuntimeTests: ParametrizedTestCase {

    /// This is our parametrized method. For this example it just print out parameter value
    func p(_ s: String) {
        print("Magic: \(s)")
    }

    override class func _qck_testMethodSelectors() -> [_QuickSelectorWrapper] {
        /// For this example we create 3 runtime tests "test_a", "test_b" and "test_c" with corresponding parameter
        return ["a", "b", "c"].map { parameter in
            /// first we wrap our test method in block that takes TestCase instance
            let block: @convention(block) (RuntimeTests) -> Void = { [=12=].p(parameter) }
            /// with help of ObjC runtime we add new test method to class
            let implementation = imp_implementationWithBlock(block)
            let selectorName = "test_\(parameter)"
            let selector = NSSelectorFromString(selectorName)
            class_addMethod(self, selector, implementation, "v@:")
            /// and return wrapped selector on new created method
            return _QuickSelectorWrapper(selector: selector)
        }
    }
}

预期输出：

Test Suite 'RuntimeTests' started at 2019-03-17 06:09:24.150
Test Case '-[ProtocolUnitTests.RuntimeTests test_a]' started.
Magic: a
Test Case '-[ProtocolUnitTests.RuntimeTests test_a]' passed (0.006 seconds).
Test Case '-[ProtocolUnitTests.RuntimeTests test_b]' started.
Magic: b
Test Case '-[ProtocolUnitTests.RuntimeTests test_b]' passed (0.001 seconds).
Test Case '-[ProtocolUnitTests.RuntimeTests test_c]' started.
Magic: c
Test Case '-[ProtocolUnitTests.RuntimeTests test_c]' passed (0.001 seconds).
Test Suite 'RuntimeTests' passed at 2019-03-17 06:09:24.159.

感谢 Quick 团队 super class implementation。

编辑：我用示例创建了 repo github

如何动态添加 XCTestCase

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