04/05: add solution code

Author: kettanaito

exercises/04.assertions/05.solution.soft-assertions/README.mdx

@@ -1,3 +1,7 @@
 # Soft assertions
 
 - Use `expect.soft()` to allow multiple assertions to fail without short-circuiting. Useful when testing compound behaviors, where other assertion failures can help you uncover the reason of the failure.
+
+- Soft assertions are useful when:
+  - You have multiple expectations toward _the same thing_. Subsequent assertions may reveal more information about the failure.
+  - You have multiple _independent_ expectations toward _different_ things. Do some action, check that (1) URL is correct; (2) Title is displayed; (3) Button is displayed. None should fail assertions that come after. You don't want to be fixing them one-by-one—that _slows down the iteration loop_.

exercises/04.assertions/05.solution.soft-assertions/src/example.test.ts

@@ -0,0 +1,26 @@
+import { User } from './user'
+import { UnlimitedPlan } from './plans'
+
+beforeAll(() => {
+	vi.useFakeTimers()
+	vi.setSystemTime(new Date('2025-12-02T00:00:00Z'))
+})
+
+afterAll(() => {
+	vi.useRealTimers()
+})
+
+test('cancels the user subscription', () => {
+	const user = new User()
+	user.subscribe(new UnlimitedPlan())
+
+	expect.soft(user.subscription.name).toBe('Unlimited')
+	expect.soft(user.subscription.kind).toBe('yearly')
+	expect.soft(user.subscription.state).toBe('active')
+	expect.soft(user.subscription.endsAt).toBeUndefined()
+
+	user.cancelSubscription()
+
+	expect.soft(user.subscription.state).toBe('cancelled')
+	expect.soft(user.subscription.endsAt).toBe('2026-01-01T00:00:00.000Z')
+})

exercises/04.assertions/05.solution.soft-assertions/src/plans.ts

@@ -0,0 +1,62 @@
+export type PlanKind = 'monthly' | 'yearly'
+
+export class Plan {
+	public name: string
+	public kind: PlanKind
+	public state: 'active' | 'cancelled'
+	public chargeAmount: number
+	public endsAt?: string
+
+	constructor(options: {
+		name: string
+		kind: PlanKind
+		chargeAmount: number
+		endsAt?: string
+	}) {
+		this.name = options.name
+		this.kind = options.kind
+		this.chargeAmount = options.chargeAmount
+		this.state = 'active'
+		this.endsAt = options.endsAt
+	}
+
+	public cancel() {
+		if (this.state !== 'active') {
+			return
+		}
+
+		this.state = 'cancelled'
+
+		const today = new Date()
+		today.setUTCDate(1)
+		today.setUTCMonth(
+			today.getUTCMonth() + 1 > 11 ? 0 : today.getUTCMonth() + 1,
+		)
+
+		if (today.getUTCMonth() === 0) {
+			today.setUTCFullYear(today.getUTCFullYear() + 1)
+		}
+
+		this.endsAt = today.toISOString()
+	}
+}
+
+export class TrialPlan extends Plan {
+	constructor() {
+		super({
+			name: 'Trial',
+			kind: 'monthly',
+			chargeAmount: 0,
+		})
+	}
+}
+
+export class UnlimitedPlan extends Plan {
+	constructor() {
+		super({
+			name: 'Unlimited',
+			kind: 'yearly',
+			chargeAmount: 250,
+		})
+	}
+}

exercises/04.assertions/05.solution.soft-assertions/src/user.ts

@@ -0,0 +1,17 @@
+import { TrialPlan, type Plan } from './plans'
+
+export class User {
+	public subscription: Plan
+
+	constructor() {
+		this.subscription = new TrialPlan()
+	}
+
+	public subscribe(subscription: Plan) {
+		this.subscription = subscription
+	}
+
+	public cancelSubscription() {
+		this.subscription.cancel()
+	}
+}

exercises/04.assertions/05.solution.soft-assertions/tsconfig.node.json

@@ -3,5 +3,5 @@
 	"compilerOptions": {
 		"lib": ["ES2023"]
 	},
-	"include": ["vite.config.ts"]
+	"include": ["vitest.config.ts"]
 }