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How to cleanly make swift-snapshot-testing run correctly in Xcode Cloud. You need to bundle the snapshots and resources into your test bundles (xctest), and then use this kind of code to instruct snapshot-testing to pick them up from the test bundle if present.
#if os(iOS)
import SnapshotTesting
import SwiftUI
import XCTest
public extension XCTestCase {
/// Test the layout of a full-screen SwiftUI view.
///
/// Currently, this is hardcoded to logical width and height of iPhone 14 Pro screen. It assumes that tests are ran only on iPhone 14 Pro simulator,
/// so you’ll need to change this also in the Xcode Cloud workflow. Change the device from “recommended iPhones” to “iPhone 14 Pro”.
///
/// This currently tests the EN and ET languages, to visually spot any problems in language localization.
///
/// - Parameters:
/// - view: The view to test.
/// - testBundleResourceURL: Resource URL that contains a folder with the reference screenshots.
/// For SPM module tests, the folder will be named `__Snapshots__/TestClassName`.
/// For top-level app target tests, the folder will be named simply `TestClassName`.
/// - file: The test file calling this function. No need to pass it, this is determined automatically.
/// - testName: Test function that is calling this function. No need to pass it, this is determined automatically.
/// - line: Line in the test file calling this function. No need to pass it, this is determined automatically.
func assertSnapshot(
view: some View,
testBundleResourceURL: URL,
file: StaticString = #file,
testName: String = #function,
line: UInt = #line
) {
let locales = [Locale(identifier: "en_US"), Locale(identifier: "et_EE")]
let testClassFileURL = URL(fileURLWithPath: "\(file)", isDirectory: false)
let testClassName = testClassFileURL.deletingPathExtension().lastPathComponent
let folderCandidates = [
// For SPM modules.
testBundleResourceURL.appending(path: "__Snapshots__").appending(path: testClassName),
// For top-level xcodeproj app target.
testBundleResourceURL.appending(path: testClassName)
]
for locale in locales {
// Default case: snapshots are not present in test bundle. This will fall back to standard SnapshotTesting behavior,
// where the snapshots live in `__Snapshots__` folder that is adjacent to the test class.
var snapshotDirectory: String? = nil
for folder in folderCandidates {
let referenceSnapshotURLInTestBundle = folder.appending(path: "\(sanitizePathComponent(testName)).\(locale.identifier).png")
if FileManager.default.fileExists(atPath: referenceSnapshotURLInTestBundle.path(percentEncoded: false)) {
// The snapshot file is present in the test bundle, so we will instruct snapshot-testing to use the folder
// pointing to the snapshots in the test bundle, instead of the default.
// This is the code path that Xcode Cloud will follow, if everything is set up correctly.
snapshotDirectory = folder.path(percentEncoded: false)
}
}
let failure = SnapshotTesting.verifySnapshot(
matching: view
.frame(width: 393, height: 852)
.environment(\.locale, locale),
// When precision is the default 100%, some snapshot tests on Xcode Cloud fail,
// even though there is no visible difference between reference and test result images,
// and the difference image is completely black (does not indicate any different pixels).
// 🤷 Just lowering the tolerance a bit seems to make it more resilient.
as: .image(precision: 0.98),
named: locale.identifier,
record: false,
snapshotDirectory: snapshotDirectory,
file: file,
testName: testName,
line: line
)
if let message = failure {
XCTFail(message, file: file, line: line)
}
}
}
// Copied from swift-snapshot-testing
func sanitizePathComponent(_ string: String) -> String {
return string
.replacingOccurrences(of: "\\W+", with: "-", options: .regularExpression)
.replacingOccurrences(of: "^-|-$", with: "", options: .regularExpression)
}
}
#endif
@jaanus
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jaanus commented Jun 20, 2023

Blog post with longer discussion: https://jaanus.com/snapshot-testing-xcode-cloud/

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