Testing Stores and Reactivity
Test Svelte stores in isolation and verify that derived values update correctly.
Testing Stores and Reactivity is a free Sveltejs Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Sveltejs Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Stores in Isolation
Test Svelte stores by importing them and asserting on their values after updates.
import { count } from "$lib/stores";
import { get } from "svelte/store";
count.set(5);
expect(get(count)).toBe(5);get Helper
get(store) reads the current value synchronously, useful in tests.
Subscribe in Tests
You can subscribe directly to capture every emitted value.
const values = [];
const unsub = count.subscribe(v => values.push(v));
count.set(1);
unsub();Derived Stores
Test derived stores by setting source values and reading the derived output.
Custom Store Methods
Call your store's custom actions and assert state.
Async Stores
For async stores, await microtasks or use vi.runAllTimers if using fake timers.
Reset Between Tests
Reset stores in beforeEach to avoid cross-test pollution.
Reactive Components
Render a component and subscribe to a store inside the test to confirm reactive updates.
Stores in Components
Combine render + store updates + assertions to test full reactive flows.
Type Safety
With TypeScript, store types flow into tests for safe assertions.
Mocks
Mock stores when isolating component logic from their data.
Quick Check
How do you read a store value in tests?
Recap
Test stores with get(store), subscriptions, and resets in beforeEach. Combine with render for component tests.
Frequently asked questions
Is the “Testing Stores and Reactivity” lesson free?
Yes — the full text of “Testing Stores and Reactivity” is free to read here on the web, and the Sveltejs Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Sveltejs Academy course, upgrade to CoddyKit PRO.
What will I learn in “Testing Stores and Reactivity”?
Test Svelte stores in isolation and verify that derived values update correctly. You practise Sveltejs Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Sveltejs Academy?
No prior experience is required. Sveltejs Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Testing Stores and Reactivity” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Sveltejs Academy lesson?
Yes. Every Sveltejs Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Vitest Setup for Svelte Projects
- @testing-library/svelte: render and fireEvent
- Testing Stores and Reactivity
- Mocking Modules and Fetch