diff --git a/packages/backend/test/unit/SigninWithPasskeyApiService.ts b/packages/backend/test/unit/SigninWithPasskeyApiService.ts
new file mode 100644
index 0000000000..bae2b88c60
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+++ b/packages/backend/test/unit/SigninWithPasskeyApiService.ts
@@ -0,0 +1,182 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { IncomingHttpHeaders } from 'node:http';
+import { afterAll, afterEach, beforeAll, beforeEach, describe, expect, jest, test } from '@jest/globals';
+import { Test, TestingModule } from '@nestjs/testing';
+import { FastifyReply, FastifyRequest } from 'fastify';
+import { AuthenticationResponseJSON } from '@simplewebauthn/types';
+import { HttpHeader } from 'fastify/types/utils.js';
+import { MockFunctionMetadata, ModuleMocker } from 'jest-mock';
+import { MiUser } from '@/models/User.js';
+import { MiUserProfile, UserProfilesRepository, UsersRepository } from '@/models/_.js';
+import { IdService } from '@/core/IdService.js';
+import { GlobalModule } from '@/GlobalModule.js';
+import { DI } from '@/di-symbols.js';
+import { CoreModule } from '@/core/CoreModule.js';
+import { SigninWithPasskeyApiService } from '@/server/api/SigninWithPasskeyApiService.js';
+import { RateLimiterService } from '@/server/api/RateLimiterService.js';
+import { WebAuthnService } from '@/core/WebAuthnService.js';
+import { SigninService } from '@/server/api/SigninService.js';
+import { IdentifiableError } from '@/misc/identifiable-error.js';
+
+const moduleMocker = new ModuleMocker(global);
+
+class FakeLimiter {
+	public async limit() {
+		return;
+	}
+}
+
+class FakeSigninService {
+	public signin(..._args: any): any {
+		return true;
+	}
+}
+
+class DummyFastifyReply {
+	public statusCode: number;
+	code(num: number): void {
+		this.statusCode = num;
+	}
+	header(_key: HttpHeader, _value: any): void {
+	}
+}
+class DummyFastifyRequest {
+	public ip: string;
+	public body: {credential: any, context: string};
+	public headers: IncomingHttpHeaders = { 'accept': 'application/json' };
+	constructor(body?: any) {
+		this.ip = '0.0.0.0';
+		this.body = body;
+	}
+}
+
+type ApiFastifyRequestType = FastifyRequest<{
+	Body: {
+		credential?: AuthenticationResponseJSON;
+		context?: string;
+	};
+}>;
+
+describe('SigninWithPasskeyApiService', () => {
+	let app: TestingModule;
+	let passkeyApiService: SigninWithPasskeyApiService;
+	let usersRepository: UsersRepository;
+	let userProfilesRepository: UserProfilesRepository;
+	let webAuthnService: WebAuthnService;
+	let idService: IdService;
+	let FakeWebauthnVerify: ()=>Promise<string>;
+
+	async function createUser(data: Partial<MiUser> = {}) {
+		const user = await usersRepository
+			.save({
+				...data,
+			});
+		return user;
+	}
+
+	async function createUserProfile(data: Partial<MiUserProfile> = {}) {
+		const userProfile = await userProfilesRepository
+			.save({ ...data },
+			);
+		return userProfile;
+	}
+
+	beforeAll(async () => {
+		app = await Test.createTestingModule({
+			imports: [GlobalModule, CoreModule],
+			providers: [
+				SigninWithPasskeyApiService, 
+				{ provide: RateLimiterService, useClass: FakeLimiter }, 
+				{ provide: SigninService, useClass: FakeSigninService },
+			],
+		}).useMocker((token) => {
+			if (typeof token === 'function') {
+				const mockMetadata = moduleMocker.getMetadata(token) as MockFunctionMetadata<any, any>;
+				const Mock = moduleMocker.generateFromMetadata(mockMetadata);
+				return new Mock();
+			}
+		}).compile();
+		passkeyApiService = app.get<SigninWithPasskeyApiService>(SigninWithPasskeyApiService);
+		usersRepository = app.get<UsersRepository>(DI.usersRepository);
+		userProfilesRepository = app.get<UserProfilesRepository>(DI.userProfilesRepository);
+		webAuthnService = app.get<WebAuthnService>(WebAuthnService);
+		idService = app.get<IdService>(IdService);
+	});
+
+	beforeEach(async () => {
+		const uid = idService.gen();
+		FakeWebauthnVerify = async () => {
+			return uid;
+		};
+		jest.spyOn(webAuthnService, 'verifySignInWithPasskeyAuthentication').mockImplementation(FakeWebauthnVerify);
+
+		const dummyUser = {
+			id: uid, username: uid, usernameLower: uid.toLocaleLowerCase(), uri: null, host: null,
+		 };
+		const dummyProfile = {
+			userId: uid,
+			password: 'qwerty',
+			usePasswordLessLogin: true,
+		};
+		await createUser(dummyUser);
+		await createUserProfile(dummyProfile);
+	});
+
+	afterAll(async () => {
+		await app.close();
+	});
+
+	describe('Get Passkey Options', () => {
+		it('Should return passkey Auth Options', async () => {
+			const req = new DummyFastifyRequest({}) as ApiFastifyRequestType;
+			const res = new DummyFastifyReply() as unknown as FastifyReply;
+			const res_body = await passkeyApiService.signin(req, res);
+			expect(res.statusCode).toBe(200);
+			expect((res_body as any).option).toBeDefined();
+			expect(typeof (res_body as any).context).toBe('string');
+		});
+	});
+	describe('Try Passkey Auth', () => {
+		it('Should Success', async () => {
+			const req = new DummyFastifyRequest({ context: 'auth-context', credential: { dummy: [] } }) as ApiFastifyRequestType;
+			const res = new DummyFastifyReply() as FastifyReply;
+			const res_body = await passkeyApiService.signin(req, res);
+			expect((res_body as any).signinResponse).toBeDefined();
+		});
+
+		it('Should return 400 Without Auth Context', async () => {
+			const req = new DummyFastifyRequest({ credential: { dummy: [] } }) as ApiFastifyRequestType;
+			const res = new DummyFastifyReply() as FastifyReply;
+			const res_body = await passkeyApiService.signin(req, res);
+			expect(res.statusCode).toBe(400);
+			expect((res_body as any).error?.id).toStrictEqual('1658cc2e-4495-461f-aee4-d403cdf073c1');
+		});
+
+		it('Should return 403 When Challenge Verify fail', async () => {
+			const req = new DummyFastifyRequest({ context: 'misskey-1234', credential: { dummy: [] } }) as ApiFastifyRequestType;
+			const res = new DummyFastifyReply() as FastifyReply;
+			jest.spyOn(webAuthnService, 'verifySignInWithPasskeyAuthentication')
+				.mockImplementation(async () => {
+					throw new IdentifiableError('THIS_ERROR_CODE_SHOULD_BE_FORWARDED');
+				});
+			const res_body = await passkeyApiService.signin(req, res);
+			expect(res.statusCode).toBe(403);
+			expect((res_body as any).error?.id).toStrictEqual('THIS_ERROR_CODE_SHOULD_BE_FORWARDED');
+		});
+
+		it('Should return 403 When The user not Enabled Passwordless login', async () => {
+			const req = new DummyFastifyRequest({ context: 'misskey-1234', credential: { dummy: [] } }) as ApiFastifyRequestType;
+			const res = new DummyFastifyReply() as FastifyReply;
+			const userId = await FakeWebauthnVerify();
+			const data = { userId: userId, usePasswordLessLogin: false };
+			await userProfilesRepository.update({ userId: userId }, data);
+			const res_body = await passkeyApiService.signin(req, res);
+			expect(res.statusCode).toBe(403);
+			expect((res_body as any).error?.id).toStrictEqual('2d84773e-f7b7-4d0b-8f72-bb69b584c912');
+		});
+	});
+});