Generate comprehensive ViewModel tests with multi-locale translation verification. Use when creating test coverage for ViewModels, especially those with localization.
Generates comprehensive ViewModel tests with multi-locale translation verification. Use when creating test coverage for ViewModels, especially those with localization.
/plugin marketplace add foscomputerservices/FOSUtilities/plugin install fosmvvm-generators@fosmvvm-toolsThis skill inherits all available tools. When active, it can use any tool Claude has access to.
Generate test files for ViewModels following FOSMVVM testing patterns.
For full architecture context, see FOSMVVMArchitecture.md
ViewModel testing in FOSMVVM verifies three critical aspects:
@LocalizedString properties have values in all supported localesThe LocalizableTestCase protocol provides infrastructure that tests all three in a single call.
@LocalizedSubs substitution behavior| File | Location | Purpose |
|---|---|---|
{Name}ViewModelTests.swift | Tests/{Target}Tests/Localization/ | Test suite conforming to LocalizableTestCase |
{Name}ViewModel.yml | Tests/{Target}Tests/TestYAML/ | YAML translations for test (if needed) |
For most ViewModels, a single line provides complete coverage:
@Test func dashboardViewModel() throws {
try expectFullViewModelTests(DashboardViewModel.self)
}
This verifies:
This is sufficient for the vast majority of ViewModel tests.
When testing specific formatting behavior (substitutions, compound strings), add locale-specific assertions:
@Test func greetingWithSubstitution() throws {
try expectFullViewModelTests(GreetingViewModel.self)
// Verify specific substitution behavior
let vm: GreetingViewModel = try .stub()
.toJSON(encoder: encoder(locale: en))
.fromJSON()
#expect(try vm.welcomeMessage.localizedString == "Welcome, John!")
}
This is optional - use only when verifying specific formatting techniques.
Test suites conform to LocalizableTestCase to access testing infrastructure:
import FOSFoundation
@testable import FOSMVVM
import FOSTesting
import Foundation
import Testing
@Suite("My ViewModel Tests")
struct MyViewModelTests: LocalizableTestCase {
let locStore: LocalizationStore
init() throws {
self.locStore = try Self.loadLocalizationStore(
bundle: Bundle.module,
resourceDirectoryName: "TestYAML"
)
}
}
| Property/Method | Purpose |
|---|---|
locStore | Required - the localization store |
locales | Optional - locales to test (default: en, es) |
encoder(locale:) | Creates a localizing JSONEncoder |
en, es, enGB, enUS | Locale constants |
| Method | Use When |
|---|---|
expectFullViewModelTests(_:) | Primary - complete ViewModel testing |
expectTranslations(_:) | Translation-only verification |
expectFullFieldValidationModelTests(_:) | Testing FieldValidationModel types |
expectFullFormFieldTests(_:) | Testing FormField instances |
expectCodable(_:encoder:) | Codable round-trip only |
expectVersionedViewModel(_:encoder:) | Versioning stability only |
Every ViewModel with @LocalizedString properties needs YAML entries:
@ViewModel
public struct DashboardViewModel: RequestableViewModel {
@LocalizedString public var pageTitle // Needs YAML entry
@LocalizedString public var emptyMessage // Needs YAML entry
public let itemCount: Int // No YAML needed
}
# DashboardViewModel.yml
en:
DashboardViewModel:
pageTitle: "Dashboard"
emptyMessage: "No items yet"
es:
DashboardViewModel:
pageTitle: "Tablero"
emptyMessage: "No hay elementos todavía"
When a ViewModel contains child ViewModels, all types in the hierarchy need YAML entries:
@ViewModel
public struct BoardViewModel: RequestableViewModel {
@LocalizedString public var title
public let cards: [CardViewModel] // Child ViewModel
}
@ViewModel
public struct CardViewModel {
@LocalizedString public var cardTitle
}
Both BoardViewModel and CardViewModel need YAML entries (can be in same or separate files).
When tests define private ViewModel structs for testing specific scenarios, those also need YAML:
// In test file
private struct TestParentViewModel: ViewModel {
@LocalizedString var title
let children: [TestChildViewModel]
}
private struct TestChildViewModel: ViewModel {
@LocalizedString var label
}
Add entries to a test YAML file for these private types.
Determine which ViewModels need test coverage:
Verify YAML entries exist for:
Create test suite conforming to LocalizableTestCase:
@Test function per ViewModel (or logical grouping)expectFullViewModelTests() as the primary assertionswift test --filter {TestSuiteName}
See reference.md for complete file templates.
@Test func dashboardViewModel() throws {
try expectFullViewModelTests(DashboardViewModel.self)
}
@Test func boardViewModels() throws {
try expectFullViewModelTests(BoardViewModel.self)
try expectFullViewModelTests(ColumnViewModel.self)
try expectFullViewModelTests(CardViewModel.self)
}
var locales: Set<Locale> { [en, es, enGB] } // Override default
@Test func multiLocaleViewModel() throws {
try expectFullViewModelTests(MyViewModel.self)
// Tests en, es, AND en-GB
}
@Test func greetingSubstitutions() throws {
try expectFullViewModelTests(GreetingViewModel.self)
let vm: GreetingViewModel = try .stub(userName: "Alice")
.toJSON(encoder: encoder(locale: en))
.fromJSON()
#expect(try vm.welcomeMessage.localizedString == "Welcome, Alice!")
}
@Test func parentWithChildren() throws {
// Tests parent AND verifies children can be encoded/decoded
try expectFullViewModelTests(ParentViewModel.self)
// Optionally verify specific child values
let vm: ParentViewModel = try .stub()
.toJSON(encoder: encoder(locale: en))
.fromJSON()
#expect(try vm.children[0].label.localizedString == "Child 1")
}
FOSLocalizableError: _pageTitle -- Missing Translation -- en
Cause: YAML entry missing for a @LocalizedString property.
Fix: Add the property to the YAML file:
en:
MyViewModel:
pageTitle: "Page Title" # Add this
Cause: The ViewModel wasn't encoded with a localizing encoder.
Fix: Ensure using encoder(locale:) or expectFullViewModelTests().
Cause: YAML values exist but may have typos or wrong content.
Fix: Add specific assertions to verify exact values:
let vm = try .stub().toJSON(encoder: encoder(locale: en)).fromJSON()
#expect(try vm.title.localizedString == "Expected Value")
| Concept | Convention | Example |
|---|---|---|
| Test suite | {Feature}ViewModelTests | DashboardViewModelTests |
| Test file | {Feature}ViewModelTests.swift | DashboardViewModelTests.swift |
| YAML file | {ViewModelName}.yml | DashboardViewModel.yml |
| Test method | {viewModelName}() or descriptive | dashboardViewModel() |
| Version | Date | Changes |
|---|---|---|
| 1.0 | 2025-01-02 | Initial skill |
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