UIKit vs SwiftUI (wrapped in UIKit) – Why Tests Fail?

[Fuyan777]

Overview

Please tell me the reason why the test fails when comparing a screen created with UIKit and a screen that wraps a SwiftUI view in UIKit.

Screenshots

Result

Code

Test

import Testing
@testable import SnapshotSample
import SnapshotTesting
import SnapshotTestingHEIC

@MainActor
struct SnapshotSampleTests {
    @Test
    func example() throws {
        let uikitView = ContentViewController()
        let swiftUIview = ContentViewWrapper()

        withSnapshotTesting(record: nil, diffTool: .ksdiff) {
            // NOTE: switching bellow code

//            assertSnapshot(of: uikitView, as: .image(on: .iPhone12))
            assertSnapshot(of: swiftUIview, as: .image(on: .iPhone12, perceptualPrecision: 0.9))
        }
    }
}

UIKit only

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundStyle(.tint)
            Text("Hello, world!!")
        }
        .padding()
        .background(Color(uiColor: .white))
    }
}

class ContentViewWrapper: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupContentView()
    }
    
    private func setupContentView() {
        let contentView = ContentView()
        let hostingController = UIHostingController(rootView: contentView)

        addChild(hostingController)
        view.addSubview(hostingController.view)
        hostingController.didMove(toParent: self)

        hostingController.view.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            hostingController.view.topAnchor.constraint(equalTo: view.topAnchor),
            hostingController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            hostingController.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            hostingController.view.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])
    }
}

SwiftUI (wrapped in UIKit)

import UIKit

class ContentViewController: UIViewController {
    
    private let stackView: UIStackView = {
        let stack = UIStackView()
        stack.axis = .vertical
        stack.alignment = .center
        stack.spacing = 8
        stack.translatesAutoresizingMaskIntoConstraints = false
        return stack
    }()
    
    private let imageView: UIImageView = {
        let imageView = UIImageView()
        let configuration = UIImage.SymbolConfiguration(scale: .large)
        imageView.image = UIImage(systemName: "globe", withConfiguration: configuration)
        imageView.tintColor = .tintColor
        imageView.contentMode = .scaleAspectFit
        return imageView
    }()
    
    private let label: UILabel = {
        let label = UILabel()
        label.text = "Hello, world!!"
        label.font = .preferredFont(forTextStyle: .body)
        return label
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupViews()
    }
    
    private func setupViews() {
        view.backgroundColor = .white
        
        // Add subviews
        view.addSubview(stackView)
        stackView.addArrangedSubview(imageView)
        stackView.addArrangedSubview(label)
        
        // Setup constraints
        NSLayoutConstraint.activate([
            stackView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            stackView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            stackView.leadingAnchor.constraint(greaterThanOrEqualTo: view.leadingAnchor, constant: 20),
            stackView.trailingAnchor.constraint(lessThanOrEqualTo: view.trailingAnchor, constant: -20)
        ])
    }
}

Sorry if this has been answered already. I couldn't find anything when I searched.