diff --git a/packages/backend/test/e2e/move.ts b/packages/backend/test/e2e/move.ts
index 67118a6bf7..8a38857b87 100644
--- a/packages/backend/test/e2e/move.ts
+++ b/packages/backend/test/e2e/move.ts
@@ -12,7 +12,7 @@ import { loadConfig } from '@/config.js';
 import { MiRepository, MiUser, UsersRepository, miRepository } from '@/models/_.js';
 import { secureRndstr } from '@/misc/secure-rndstr.js';
 import { jobQueue } from '@/boot/common.js';
-import { api, initTestDb, signup, sleep, successfulApiCall, uploadFile } from '../utils.js';
+import { api, castAsError, initTestDb, signup, sleep, successfulApiCall, uploadFile } from '../utils.js';
 import type * as misskey from 'misskey-js';
 
 describe('Account Move', () => {
@@ -92,8 +92,8 @@ describe('Account Move', () => {
 			}, bob);
 
 			assert.strictEqual(res.status, 400);
-			assert.strictEqual(res.body.error.code, 'NO_SUCH_USER');
-			assert.strictEqual(res.body.error.id, 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5');
+			assert.strictEqual(castAsError(res.body).error.code, 'NO_SUCH_USER');
+			assert.strictEqual(castAsError(res.body).error.id, 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5');
 		});
 
 		test('Unable to add duplicated aliases to alsoKnownAs', async () => {
@@ -102,8 +102,8 @@ describe('Account Move', () => {
 			}, bob);
 
 			assert.strictEqual(res.status, 400);
-			assert.strictEqual(res.body.error.code, 'INVALID_PARAM');
-			assert.strictEqual(res.body.error.id, '3d81ceae-475f-4600-b2a8-2bc116157532');
+			assert.strictEqual(castAsError(res.body).error.code, 'INVALID_PARAM');
+			assert.strictEqual(castAsError(res.body).error.id, '3d81ceae-475f-4600-b2a8-2bc116157532');
 		});
 
 		test('Unable to add itself', async () => {
@@ -112,8 +112,8 @@ describe('Account Move', () => {
 			}, bob);
 
 			assert.strictEqual(res.status, 400);
-			assert.strictEqual(res.body.error.code, 'FORBIDDEN_TO_SET_YOURSELF');
-			assert.strictEqual(res.body.error.id, '25c90186-4ab0-49c8-9bba-a1fa6c202ba4');
+			assert.strictEqual(castAsError(res.body).error.code, 'FORBIDDEN_TO_SET_YOURSELF');
+			assert.strictEqual(castAsError(res.body).error.id, '25c90186-4ab0-49c8-9bba-a1fa6c202ba4');
 		});
 
 		test('Unable to add a nonexisting local account to alsoKnownAs', async () => {
@@ -122,16 +122,16 @@ describe('Account Move', () => {
 			}, bob);
 
 			assert.strictEqual(res1.status, 400);
-			assert.strictEqual(res1.body.error.code, 'NO_SUCH_USER');
-			assert.strictEqual(res1.body.error.id, 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5');
+			assert.strictEqual(castAsError(res1.body).error.code, 'NO_SUCH_USER');
+			assert.strictEqual(castAsError(res1.body).error.id, 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5');
 
 			const res2 = await api('i/update', {
 				alsoKnownAs: ['@alice', 'nonexist'],
 			}, bob);
 
 			assert.strictEqual(res2.status, 400);
-			assert.strictEqual(res2.body.error.code, 'NO_SUCH_USER');
-			assert.strictEqual(res2.body.error.id, 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5');
+			assert.strictEqual(castAsError(res2.body).error.code, 'NO_SUCH_USER');
+			assert.strictEqual(castAsError(res2.body).error.id, 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5');
 		});
 
 		test('Able to add two existing local account to alsoKnownAs', async () => {
@@ -240,8 +240,8 @@ describe('Account Move', () => {
 			}, root);
 
 			assert.strictEqual(res.status, 400);
-			assert.strictEqual(res.body.error.code, 'NOT_ROOT_FORBIDDEN');
-			assert.strictEqual(res.body.error.id, '4362e8dc-731f-4ad8-a694-be2a88922a24');
+			assert.strictEqual(castAsError(res.body).error.code, 'NOT_ROOT_FORBIDDEN');
+			assert.strictEqual(castAsError(res.body).error.id, '4362e8dc-731f-4ad8-a694-be2a88922a24');
 		});
 
 		test('Unable to move to a nonexisting local account', async () => {
@@ -250,8 +250,8 @@ describe('Account Move', () => {
 			}, alice);
 
 			assert.strictEqual(res.status, 400);
-			assert.strictEqual(res.body.error.code, 'NO_SUCH_USER');
-			assert.strictEqual(res.body.error.id, 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5');
+			assert.strictEqual(castAsError(res.body).error.code, 'NO_SUCH_USER');
+			assert.strictEqual(castAsError(res.body).error.id, 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5');
 		});
 
 		test('Unable to move if alsoKnownAs is invalid', async () => {
@@ -260,8 +260,8 @@ describe('Account Move', () => {
 			}, alice);
 
 			assert.strictEqual(res.status, 400);
-			assert.strictEqual(res.body.error.code, 'DESTINATION_ACCOUNT_FORBIDS');
-			assert.strictEqual(res.body.error.id, 'b5c90186-4ab0-49c8-9bba-a1f766282ba4');
+			assert.strictEqual(castAsError(res.body).error.code, 'DESTINATION_ACCOUNT_FORBIDS');
+			assert.strictEqual(castAsError(res.body).error.id, 'b5c90186-4ab0-49c8-9bba-a1f766282ba4');
 		});
 
 		test('Relationships have been properly migrated', async () => {
@@ -307,6 +307,7 @@ describe('Account Move', () => {
 			const rootLists = await api('users/lists/list', {}, root);
 			assert.strictEqual(rootLists.status, 200);
 			assert.ok(rootLists);
+			assert.ok(rootLists.body[0].userIds);
 			assert.strictEqual(rootLists.body[0].userIds.length, 2);
 			assert.ok(rootLists.body[0].userIds.find((id: string) => id === bob.id));
 			assert.ok(rootLists.body[0].userIds.find((id: string) => id === alice.id));
@@ -314,6 +315,7 @@ describe('Account Move', () => {
 			const eveLists = await api('users/lists/list', {}, eve);
 			assert.strictEqual(eveLists.status, 200);
 			assert.ok(eveLists);
+			assert.ok(eveLists.body[0].userIds);
 			assert.strictEqual(eveLists.body[0].userIds.length, 1);
 			assert.ok(eveLists.body[0].userIds.find((id: string) => id === bob.id));
 		});
@@ -352,8 +354,8 @@ describe('Account Move', () => {
 			}, bob);
 
 			assert.strictEqual(res.status, 400);
-			assert.strictEqual(res.body.error.code, 'DESTINATION_ACCOUNT_FORBIDS');
-			assert.strictEqual(res.body.error.id, 'b5c90186-4ab0-49c8-9bba-a1f766282ba4');
+			assert.strictEqual(castAsError(res.body).error.code, 'DESTINATION_ACCOUNT_FORBIDS');
+			assert.strictEqual(castAsError(res.body).error.id, 'b5c90186-4ab0-49c8-9bba-a1f766282ba4');
 		});
 
 		test('Follow and follower counts are properly adjusted', async () => {
@@ -424,8 +426,9 @@ describe('Account Move', () => {
 		] as const)('Prohibit access after moving: %s', async (endpoint) => {
 			const res = await api(endpoint, {}, alice);
 			assert.strictEqual(res.status, 403);
-			assert.strictEqual(res.body.error.code, 'YOUR_ACCOUNT_MOVED');
-			assert.strictEqual(res.body.error.id, '56f20ec9-fd06-4fa5-841b-edd6d7d4fa31');
+			assert.ok(res.body);
+			assert.strictEqual(castAsError(res.body).error.code, 'YOUR_ACCOUNT_MOVED');
+			assert.strictEqual(castAsError(res.body).error.id, '56f20ec9-fd06-4fa5-841b-edd6d7d4fa31');
 		});
 
 		test('Prohibit access after moving: /antennas/update', async () => {
@@ -443,17 +446,19 @@ describe('Account Move', () => {
 			}, alice);
 
 			assert.strictEqual(res.status, 403);
-			assert.strictEqual(res.body.error.code, 'YOUR_ACCOUNT_MOVED');
-			assert.strictEqual(res.body.error.id, '56f20ec9-fd06-4fa5-841b-edd6d7d4fa31');
+			assert.ok(res.body);
+			assert.strictEqual(castAsError(res.body).error.code, 'YOUR_ACCOUNT_MOVED');
+			assert.strictEqual(castAsError(res.body).error.id, '56f20ec9-fd06-4fa5-841b-edd6d7d4fa31');
 		});
 
 		test('Prohibit access after moving: /drive/files/create', async () => {
 			// FIXME: 一旦逃げておく
-			const res = await uploadFile(alice) as any;
+			const res = await uploadFile(alice);
 
 			assert.strictEqual(res.status, 403);
-			assert.strictEqual((res.body! as any as { error: misskey.api.APIError }).error.code, 'YOUR_ACCOUNT_MOVED');
-			assert.strictEqual((res.body! as any as { error: misskey.api.APIError }).error.id, '56f20ec9-fd06-4fa5-841b-edd6d7d4fa31');
+			assert.ok(res.body);
+			assert.strictEqual(castAsError(res.body).error.code, 'YOUR_ACCOUNT_MOVED');
+			assert.strictEqual(castAsError(res.body).error.id, '56f20ec9-fd06-4fa5-841b-edd6d7d4fa31');
 		});
 
 		test('Prohibit updating alsoKnownAs after moving', async () => {
@@ -462,8 +467,8 @@ describe('Account Move', () => {
 			}, alice);
 
 			assert.strictEqual(res.status, 403);
-			assert.strictEqual(res.body.error.code, 'YOUR_ACCOUNT_MOVED');
-			assert.strictEqual(res.body.error.id, '56f20ec9-fd06-4fa5-841b-edd6d7d4fa31');
+			assert.strictEqual(castAsError(res.body).error.code, 'YOUR_ACCOUNT_MOVED');
+			assert.strictEqual(castAsError(res.body).error.id, '56f20ec9-fd06-4fa5-841b-edd6d7d4fa31');
 		});
 	});
 });
diff --git a/packages/backend/test/utils.ts b/packages/backend/test/utils.ts
index a04a20c478..0b50d628bf 100644
--- a/packages/backend/test/utils.ts
+++ b/packages/backend/test/utils.ts
@@ -17,6 +17,7 @@ import { validateContentTypeSetAsActivityPub } from '@/core/activitypub/misc/val
 import { entities } from '../src/postgres.js';
 import { loadConfig } from '../src/config.js';
 import type * as misskey from 'misskey-js';
+import { ApiError } from "@/server/api/error.js";
 
 export { server as startServer, jobQueue as startJobQueue } from '@/boot/common.js';
 
@@ -644,3 +645,9 @@ export async function sendEnvResetRequest() {
 		throw new Error('server env update failed.');
 	}
 }
+
+// 与えられた値を強制的にエラーとみなす。この関数は型安全性を破壊するため、異常系のアサーション以外で用いられるべきではない。
+// FIXME(misskey-js): misskey-jsがエラー情報を公開するようになったらこの関数を廃止する
+export function castAsError(obj: Record<string, unknown>): { error: ApiError } {
+	return obj as { error: ApiError };
+}