问为什么单元测试中的代码不能找到包资源？

EN

NSBundle *bundle = [NSBundle bundleForClass:[self class]];
NSString *path = [bundle pathForResource:@"foo" ofType:@"txt"];

let testBundle = NSBundle(forClass: self.dynamicType)
let fileURL = testBundle.URLForResource("imageName", withExtension: "png")
XCTAssertNotNil(fileURL)

let testBundle = Bundle(for: type(of: self))
let filePath = testBundle.path(forResource: "imageName", ofType: "png")
XCTAssertNotNil(filePath)

@testable import Example

class ExampleTests: XCTestCase {
        
    func testExample() {
        let bundleMain = Bundle.main
        let bundleDoingTest = Bundle(for: type(of: self ))
        let bundleBeingTested = Bundle(identifier: "com.example.Example")!
                
        print("bundleMain.bundlePath : \(bundleMain.bundlePath)")
        // …/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Xcode/Agents
        print("bundleDoingTest.bundlePath : \(bundleDoingTest.bundlePath)")
        // …/PATH/TO/Debug/ExampleTests.xctest
        print("bundleBeingTested.bundlePath : \(bundleBeingTested.bundlePath)")
        // …/PATH/TO/Debug/Example.app
        
        print("bundleMain = " + bundleMain.description) // Xcode Test Agent
        print("bundleDoingTest = " + bundleDoingTest.description) // Test Case Bundle
        print("bundleUnderTest = " + bundleBeingTested.description) // App Bundle

/Users/
  UserName/
    Library/
      Developer/
        Xcode/
          DerivedData/
            App-qwertyuiop.../
              Build/
                Products/
                  Debug-iphonesimulator/
                    AppTests.xctest/
                      foo.txt

/Users/
  UserName/
    Library/
    Developer/
      CoreSimulator/
        Devices/
          _UUID_/
            data/
              Containers/
                Bundle/
                  Application/
                    _UUID_/
                      App.app/

let testBundle = Bundle(for: type(of: self)) 
print("testBundle.bundlePath = \(testBundle.bundlePath) ")

// swift-tools-version:5.3
import PackageDescription

  targets: [
    .target(
      name: "CLIQuickstartLib",
      dependencies: [],
      resources: [
        // Apply platform-specific rules.
        // For example, images might be optimized per specific platform rule.
        // If path is a directory, the rule is applied recursively.
        // By default, a file will be copied if no rule applies.
        .process("Resources"),
      ]),
    .testTarget(
      name: "CLIQuickstartLibTests",
      dependencies: [],
      resources: [
        // Copy directories as-is. 
        // Use to retain directory structure.
        // Will be at top level in bundle.
        .copy("Resources"),
      ]),

#if Xcode 
extension Foundation.Bundle {
  
  /// Returns resource bundle as a `Bundle`.
  /// Requires Xcode copy phase to locate files into `*.bundle`
  /// or `ExecutableNameTests.bundle` for test resources
  static var module: Bundle = {
    var thisModuleName = "CLIQuickstartLib"
    var url = Bundle.main.bundleURL
    
    for bundle in Bundle.allBundles 
      where bundle.bundlePath.hasSuffix(".xctest") {
      url = bundle.bundleURL.deletingLastPathComponent()
      thisModuleName = thisModuleName.appending("Tests")
    }
    
    url = url.appendingPathComponent("\(thisModuleName).bundle")
    
    guard let bundle = Bundle(url: url) else {
      fatalError("Bundle.module could not load: \(url.path)")
    }
    
    return bundle
  }()
  
  /// Directory containing resource bundle
  static var moduleDir: URL = {
    var url = Bundle.main.bundleURL
    for bundle in Bundle.allBundles 
      where bundle.bundlePath.hasSuffix(".xctest") {
      // remove 'ExecutableNameTests.xctest' path component
      url = bundle.bundleURL.deletingLastPathComponent()
    }
    return url
  }()
  
}
#endif

let testBundle = Bundle(for: type(of: self))
let fooTxtPath = testBundle.path(forResource: "foo", ofType: "txt")

let fooTxtURL = testBundle.url(forResource: "foo", withExtension: "txt")