Testing

npm install -D vitest

import { function defineConfig(config: UserConfig): UserConfig (+3 overloads)defineConfig } from 'vitest/config';

export default function defineConfig(config: UserConfig): UserConfig (+3 overloads)defineConfig({
	// ...
	// Tell Vitest to use the `browser` entry points in `package.json` files, even though it's running in Node
	
UserConfig.resolve?: (ResolveOptions & {
    alias?: AliasOptions;
}) | undefined
Configure resolver
resolve: var process: NodeJS.Processprocess.NodeJS.Process.env: NodeJS.ProcessEnv
The process.env property returns an object containing the user environment.
See environ(7).
An example of this object looks like:
{
  TERM: 'xterm-256color',
  SHELL: '/usr/local/bin/bash',
  USER: 'maciej',
  PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
  PWD: '/Users/maciej',
  EDITOR: 'vim',
  SHLVL: '1',
  HOME: '/Users/maciej',
  LOGNAME: 'maciej',
  _: '/usr/local/bin/node'
}
It is possible to modify this object, but such modifications will not be
reflected outside the Node.js process, or (unless explicitly requested)
to other Worker threads.
In other words, the following example would not work:
node -e 'process.env.foo = "bar"' && echo $foo
While the following will:
import { env } from 'node:process';

env.foo = 'bar';
console.log(env.foo);
Assigning a property on process.env will implicitly convert the value
to a string. This behavior is deprecated. Future versions of Node.js may
throw an error when the value is not a string, number, or boolean.
import { env } from 'node:process';

env.test = null;
console.log(env.test);
// => 'null'
env.test = undefined;
console.log(env.test);
// => 'undefined'
Use delete to delete a property from process.env.
import { env } from 'node:process';

env.TEST = 1;
delete env.TEST;
console.log(env.TEST);
// => undefined
On Windows operating systems, environment variables are case-insensitive.
import { env } from 'node:process';

env.TEST = 1;
console.log(env.test);
// => 1
Unless explicitly specified when creating a Worker instance,
each Worker thread has its own copy of process.env, based on its
parent thread’s process.env, or whatever was specified as the env option
to the Worker constructor. Changes to process.env will not be visible
across Worker threads, and only the main thread can make changes that
are visible to the operating system or to native add-ons. On Windows, a copy of process.env on a Worker instance operates in a case-sensitive manner
unlike the main thread.
@sincev0.1.27env.string | undefinedVITEST
		? {
				ResolveOptions.conditions?: string[] | undefinedconditions: ['browser']
			}
		: var undefinedundefined
});

import { function flushSync(fn?: (() => void) | undefined): void
Synchronously flushes any pending state changes and those that result from it.
flushSync } from 'svelte';
import { const expect: ExpectStaticexpect, const test: TestAPI
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test } from 'vitest';
import { import multipliermultiplier } from './multiplier.js';

test<object>(name: string | Function, fn?: TestFunction<object> | undefined, options?: number | TestOptions): void (+2 overloads)
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test('Multiplier', () => {
	let let double: anydouble = import multipliermultiplier(0, 2);

	expect<any>(actual: any, message?: string): Assertion<any> (+1 overload)expect(let double: anydouble.value).JestAssertion<any>.toEqual: <number>(expected: number) => voidtoEqual(0);

	let double: anydouble.set(5);

	expect<any>(actual: any, message?: string): Assertion<any> (+1 overload)expect(let double: anydouble.value).JestAssertion<any>.toEqual: <number>(expected: number) => voidtoEqual(10);
});

import { function flushSync(fn?: (() => void) | undefined): void
Synchronously flushes any pending state changes and those that result from it.
flushSync } from 'svelte';
import { const expect: ExpectStaticexpect, const test: TestAPI
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test } from 'vitest';
import { import multipliermultiplier } from './multiplier.svelte.js';

test<object>(name: string | Function, fn?: TestFunction<object> | undefined, options?: number | TestOptions): void (+2 overloads)
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test('Multiplier', () => {
	let let count: numbercount = 
function $state<0>(initial: 0): 0 (+1 overload)
namespace $state
Declares reactive state.
Example:
let count = $state(0);
https://svelte-5-preview.vercel.app/docs/runes#$state
@paraminitial The initial value$state(0);
	let let double: anydouble = import multipliermultiplier(() => let count: numbercount, 2);

	expect<any>(actual: any, message?: string): Assertion<any> (+1 overload)expect(let double: anydouble.value).JestAssertion<any>.toEqual: <number>(expected: number) => voidtoEqual(0);

	let count: numbercount = 5;

	expect<any>(actual: any, message?: string): Assertion<any> (+1 overload)expect(let double: anydouble.value).JestAssertion<any>.toEqual: <number>(expected: number) => voidtoEqual(10);
});

import { function flushSync(fn?: (() => void) | undefined): void
Synchronously flushes any pending state changes and those that result from it.
flushSync } from 'svelte';
import { const expect: ExpectStaticexpect, const test: TestAPI
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test } from 'vitest';
import { import loggerlogger } from './logger.svelte.js';

test<object>(name: string | Function, fn?: TestFunction<object> | undefined, options?: number | TestOptions): void (+2 overloads)
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test('Effect', () => {
	const const cleanup: () => voidcleanup = 
namespace $effect
function $effect(fn: () => void | (() => void)): void
Runs code when a component is mounted to the DOM, and then whenever its dependencies change, i.e. $state or $derived values.
The timing of the execution is after the DOM has been updated.
Example:
$effect(() => console.log('The count is now ' + count));
If you return a function from the effect, it will be called right before the effect is run again, or when the component is unmounted.
Does not run during server side rendering.
https://svelte-5-preview.vercel.app/docs/runes#$effect
@paramfn The function to execute$effect.function $effect.root(fn: () => void | (() => void)): () => void
The $effect.root rune is an advanced feature that creates a non-tracked scope that doesn’t auto-cleanup. This is useful for
nested effects that you want to manually control. This rune also allows for creation of effects outside of the component
initialisation phase.
Example:
&#x3C;script>
  let count = $state(0);

  const cleanup = $effect.root(() => {
	$effect(() => {
			console.log(count);
		})

	 return () => {
	   console.log('effect root cleanup');
			}
  });
&#x3C;/script>

&#x3C;button onclick={() => cleanup()}>cleanup&#x3C;/button>
https://svelte-5-preview.vercel.app/docs/runes#$effect-root
root(() => {
		let let count: numbercount = 
function $state<0>(initial: 0): 0 (+1 overload)
namespace $state
Declares reactive state.
Example:
let count = $state(0);
https://svelte-5-preview.vercel.app/docs/runes#$state
@paraminitial The initial value$state(0);

		// logger uses an $effect to log updates of its input
		let let log: anylog = import loggerlogger(() => let count: numbercount);

		// effects normally run after a microtask,
		// use flushSync to execute all pending effects synchronously
		function flushSync(fn?: (() => void) | undefined): void
Synchronously flushes any pending state changes and those that result from it.
flushSync();
		expect<any>(actual: any, message?: string): Assertion<any> (+1 overload)expect(let log: anylog.value).JestAssertion<any>.toEqual: <number[]>(expected: number[]) => voidtoEqual([0]);

		let count: numbercount = 1;
		function flushSync(fn?: (() => void) | undefined): void
Synchronously flushes any pending state changes and those that result from it.
flushSync();

		expect<any>(actual: any, message?: string): Assertion<any> (+1 overload)expect(let log: anylog.value).JestAssertion<any>.toEqual: <number[]>(expected: number[]) => voidtoEqual([0, 1]);
	});

	const cleanup: () => voidcleanup();
});

npm install -D jsdom

import { function defineConfig(config: UserConfig): UserConfig (+3 overloads)defineConfig } from 'vitest/config';

export default function defineConfig(config: UserConfig): UserConfig (+3 overloads)defineConfig({
	UserConfig.plugins?: PluginOption[] | undefined
Array of vite plugins to use.
plugins: [
		/* ... */
	],
	UserConfig.test?: InlineConfig | undefined
Options for Vitest
test: {
		// If you are testing components client-side, you need to setup a DOM environment.
		// If not all your files should have this environment, you can use a
		// `// @vitest-environment jsdom` comment at the top of the test files instead.
		InlineConfig.environment?: VitestEnvironment | undefined
Running environment
Supports ‘node’, ‘jsdom’, ‘happy-dom’, ‘edge-runtime’
If used unsupported string, will try to load the package vitest-environment-${env}
@default'node'environment: 'jsdom'
	},
	// Tell Vitest to use the `browser` entry points in `package.json` files, even though it's running in Node
	
UserConfig.resolve?: (ResolveOptions & {
    alias?: AliasOptions;
}) | undefined
Configure resolver
resolve: var process: NodeJS.Processprocess.NodeJS.Process.env: NodeJS.ProcessEnv
The process.env property returns an object containing the user environment.
See environ(7).
An example of this object looks like:
{
  TERM: 'xterm-256color',
  SHELL: '/usr/local/bin/bash',
  USER: 'maciej',
  PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
  PWD: '/Users/maciej',
  EDITOR: 'vim',
  SHLVL: '1',
  HOME: '/Users/maciej',
  LOGNAME: 'maciej',
  _: '/usr/local/bin/node'
}
It is possible to modify this object, but such modifications will not be
reflected outside the Node.js process, or (unless explicitly requested)
to other Worker threads.
In other words, the following example would not work:
node -e 'process.env.foo = "bar"' && echo $foo
While the following will:
import { env } from 'node:process';

env.foo = 'bar';
console.log(env.foo);
Assigning a property on process.env will implicitly convert the value
to a string. This behavior is deprecated. Future versions of Node.js may
throw an error when the value is not a string, number, or boolean.
import { env } from 'node:process';

env.test = null;
console.log(env.test);
// => 'null'
env.test = undefined;
console.log(env.test);
// => 'undefined'
Use delete to delete a property from process.env.
import { env } from 'node:process';

env.TEST = 1;
delete env.TEST;
console.log(env.TEST);
// => undefined
On Windows operating systems, environment variables are case-insensitive.
import { env } from 'node:process';

env.TEST = 1;
console.log(env.test);
// => 1
Unless explicitly specified when creating a Worker instance,
each Worker thread has its own copy of process.env, based on its
parent thread’s process.env, or whatever was specified as the env option
to the Worker constructor. Changes to process.env will not be visible
across Worker threads, and only the main thread can make changes that
are visible to the operating system or to native add-ons. On Windows, a copy of process.env on a Worker instance operates in a case-sensitive manner
unlike the main thread.
@sincev0.1.27env.string | undefinedVITEST
		? {
				ResolveOptions.conditions?: string[] | undefinedconditions: ['browser']
			}
		: var undefinedundefined
});

import { function flushSync(fn?: (() => void) | undefined): void
Synchronously flushes any pending state changes and those that result from it.
flushSync, 
function mount<Props extends Record<string, any>, Exports extends Record<string, any>>(component: ComponentType<SvelteComponent<Props>> | Component<Props, Exports, any>, options: {} extends Props ? {
    target: Document | Element | ShadowRoot;
    anchor?: Node;
    props?: Props;
    events?: Record<string, (e: any) => any>;
    context?: Map<any, any>;
    intro?: boolean;
} : {
    target: Document | Element | ShadowRoot;
    props: Props;
    anchor?: Node;
    events?: Record<string, (e: any) => any>;
    context?: Map<any, any>;
    intro?: boolean;
}): Exports
Mounts a component to the given target and returns the exports and potentially the props (if compiled with accessors: true) of the component.
Transitions will play during the initial render unless the intro option is set to false.
mount, function unmount(component: Record<string, any>): void
Unmounts a component that was previously mounted using mount or hydrate.
unmount } from 'svelte';
import { const expect: ExpectStaticexpect, const test: TestAPI
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test } from 'vitest';
import 
type Component = SvelteComponent<Record<string, any>, any, any>
const Component: ComponentTypeComponent from './Component.svelte';

test<object>(name: string | Function, fn?: TestFunction<object> | undefined, options?: number | TestOptions): void (+2 overloads)
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test('Component', () => {
	// Instantiate the component using Svelte's `mount` API
	const 
const component: {
    $on?(type: string, callback: (e: any) => void): () => void;
    $set?(props: Partial<Record<string, any>>): void;
} & Record<string, any>component = 
mount<Record<string, any>, {
    $on?(type: string, callback: (e: any) => void): () => void;
    $set?(props: Partial<Record<string, any>>): void;
} & Record<...>>(component: ComponentType<...> | Component<...>, options: {
    ...;
}): {
    ...;
} & Record<...>
Mounts a component to the given target and returns the exports and potentially the props (if compiled with accessors: true) of the component.
Transitions will play during the initial render unless the intro option is set to false.
mount(const Component: ComponentTypeComponent, {
		target: Document | Element | ShadowRoottarget: var document: Document
MDN Reference
document.Document.body: HTMLElement
Specifies the beginning and end of the document body.
MDN Reference
body, // `document` exists because of jsdom
		props?: Record<string, any> | undefinedprops: { initial: numberinitial: 0 }
	});

	expect<string>(actual: string, message?: string): Assertion<string> (+1 overload)expect(var document: Document
MDN Reference
document.Document.body: HTMLElement
Specifies the beginning and end of the document body.
MDN Reference
body.InnerHTML.innerHTML: string
MDN Reference
innerHTML).JestAssertion<string>.toBe: <string>(expected: string) => voidtoBe('<button>0</button>');

	// Click the button, then flush the changes so you can synchronously write expectations
	var document: Document
MDN Reference
document.Document.body: HTMLElement
Specifies the beginning and end of the document body.
MDN Reference
body.ParentNode.querySelector<"button">(selectors: "button"): HTMLButtonElement | null (+4 overloads)
Returns the first element that is a descendant of node that matches selectors.
MDN Reference
querySelector('button').HTMLElement.click(): void
MDN Reference
click();
	function flushSync(fn?: (() => void) | undefined): void
Synchronously flushes any pending state changes and those that result from it.
flushSync();

	expect<string>(actual: string, message?: string): Assertion<string> (+1 overload)expect(var document: Document
MDN Reference
document.Document.body: HTMLElement
Specifies the beginning and end of the document body.
MDN Reference
body.InnerHTML.innerHTML: string
MDN Reference
innerHTML).JestAssertion<string>.toBe: <string>(expected: string) => voidtoBe('<button>1</button>');

	// Remove the component from the DOM
	function unmount(component: Record<string, any>): void
Unmounts a component that was previously mounted using mount or hydrate.
unmount(
const component: {
    $on?(type: string, callback: (e: any) => void): () => void;
    $set?(props: Partial<Record<string, any>>): void;
} & Record<string, any>component);
});

import { function render<C extends unknown, Q extends Queries = typeof import("/vercel/path0/node_modules/.pnpm/@testing-library+dom@10.4.0/node_modules/@testing-library/dom/types/queries")>(Component: ComponentType<...>, options?: SvelteComponentOptions<C>, renderOptions?: RenderOptions<Q>): RenderResult<C, Q>
Render a component into the document.
@template{import('./component-types.js').Component} C
@template{import('@testing-library/dom').Queries} [Q=typeof import('@testing-library/dom').queries]
@paramComponent - The component to render.
@paramoptions - Customize how Svelte renders the component.
@paramrenderOptions - Customize how Testing Library sets up the document and binds queries.
@returnsThe rendered component and bound testing functions.render, const screen: Screen<typeof import("/vercel/path0/node_modules/.pnpm/@testing-library+dom@10.4.0/node_modules/@testing-library/dom/types/queries")>screen } from '@testing-library/svelte';
import 
const userEvent: {
    readonly setup: typeof setupMain;
    readonly clear: typeof clear;
    readonly click: typeof click;
    readonly copy: typeof copy;
    ... 12 more ...;
    readonly tab: typeof tab;
}userEvent from '@testing-library/user-event';
import { const expect: ExpectStaticexpect, const test: TestAPI
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test } from 'vitest';
import 
type Component = SvelteComponent<Record<string, any>, any, any>
const Component: ComponentTypeComponent from './Component.svelte';

test<object>(name: string | Function, fn?: TestFunction<object> | undefined, options?: number | TestOptions): void (+2 overloads)
Defines a test case with a given name and test function. The test function can optionally be configured with test options.
@paramname - The name of the test or a function that will be used as a test name.
@paramoptionsOrFn - Optional. The test options or the test function if no explicit name is provided.
@paramoptionsOrTest - Optional. The test function or options, depending on the previous parameters.
@throwsError If called inside another test function.
@examplets // Define a simple test test('should add two numbers', () => {   expect(add(1, 2)).toBe(3); }); 
@examplets // Define a test with options test('should subtract two numbers', { retry: 3 }, () => {   expect(subtract(5, 2)).toBe(3); }); test('Component', async () => {
	const const user: UserEventuser = 
const userEvent: {
    readonly setup: typeof setupMain;
    readonly clear: typeof clear;
    readonly click: typeof click;
    readonly copy: typeof copy;
    ... 12 more ...;
    readonly tab: typeof tab;
}userEvent.setup: (options?: Options) => UserEvent
Start a “session” with userEvent.
All APIs returned by this function share an input device state and a default configuration.
setup();
	render<SvelteComponent<Record<string, any>, any, any>, typeof import("/vercel/path0/node_modules/.pnpm/@testing-library+dom@10.4.0/node_modules/@testing-library/dom/types/queries")>(Component: ComponentType<...>, options?: SvelteComponentOptions<...> | undefined, renderOptions?: RenderOptions<...> | undefined): RenderResult<...>
Render a component into the document.
@template{import('./component-types.js').Component} C
@template{import('@testing-library/dom').Queries} [Q=typeof import('@testing-library/dom').queries]
@paramComponent - The component to render.
@paramoptions - Customize how Svelte renders the component.
@paramrenderOptions - Customize how Testing Library sets up the document and binds queries.
@returnsThe rendered component and bound testing functions.render(const Component: ComponentTypeComponent);

	const const button: HTMLElementbutton = const screen: Screen<typeof import("/vercel/path0/node_modules/.pnpm/@testing-library+dom@10.4.0/node_modules/@testing-library/dom/types/queries")>screen.getByRole<HTMLElement>(role: ByRoleMatcher, options?: ByRoleOptions | undefined): HTMLElement (+1 overload)getByRole('button');
	expect<HTMLElement>(actual: HTMLElement, message?: string): Assertion<HTMLElement> (+1 overload)expect(const button: HTMLElementbutton).toHaveTextContent(0);

	await const user: UserEventuser.click: (element: Element) => Promise<void>click(const button: HTMLElementbutton);
	expect<HTMLElement>(actual: HTMLElement, message?: string): Assertion<HTMLElement> (+1 overload)expect(const button: HTMLElementbutton).toHaveTextContent(1);
});

const 
const config: {
    webServer: {
        command: string;
        port: number;
    };
    testDir: string;
    testMatch: RegExp;
}config = {
	
webServer: {
    command: string;
    port: number;
}webServer: {
		command: stringcommand: 'npm run build && npm run preview',
		port: numberport: 4173
	},
	testDir: stringtestDir: 'tests',
	testMatch: RegExptestMatch: /(.+\.)?(test|spec)\.[jt]s/
};

export default 
const config: {
    webServer: {
        command: string;
        port: number;
    };
    testDir: string;
    testMatch: RegExp;
}config;

import { import expectexpect, import testtest } from '@playwright/test';

import testtest('home page has expected h1', async ({ page }) => {
	await page: anypage.goto('/');
	await import expectexpect(page: anypage.locator('h1')).toBeVisible();
});