test: enrich coverage for queryKeys, BaseQueryStore, and BatchFontStore

- queryKeys: add mutation-safety test for batch(), key hierarchy tests
  (list/batch/detail keys rooted in their parent base keys), and
  unique-key test for different detail IDs
- BaseQueryStore: add initial-state test (data undefined, isError false
  before any fetch resolves)
- BatchFontStore: add FontResponseError type assertion on malformed
  response, null error assertion on success, and setIds([]) disables
  query and returns empty fonts without triggering a fetch

src/entities/Font/model/store/batchFontStore.test.ts

@@ -8,7 +8,10 @@ import {
     vi,
 } from 'vitest';
 import * as api from '../../api/proxy/proxyFonts';
-import { FontNetworkError } from '../../lib/errors/errors';
+import {
+    FontNetworkError,
+    FontResponseError,
+} from '../../lib/errors/errors';
 import { BatchFontStore } from './batchFontStore.svelte';
 
 describe('BatchFontStore', () => {
@@ -58,6 +61,31 @@ describe('BatchFontStore', () => {
             vi.spyOn(api, 'fetchFontsByIds').mockResolvedValue(null as any);
             const store = new BatchFontStore(['a']);
             await vi.waitFor(() => expect(store.isError).toBe(true), { timeout: 1000 });
+            expect(store.error).toBeInstanceOf(FontResponseError);
+        });
+
+        it('should have null error in success state', async () => {
+            const fonts = [{ id: 'a' }] as any[];
+            vi.spyOn(api, 'fetchFontsByIds').mockResolvedValue(fonts);
+            const store = new BatchFontStore(['a']);
+            await vi.waitFor(() => expect(store.fonts).toEqual(fonts), { timeout: 1000 });
+            expect(store.error).toBeNull();
+        });
+    });
+
+    describe('Disable Behavior', () => {
+        it('should return empty fonts and not fetch when setIds is called with empty array', async () => {
+            const fonts1 = [{ id: 'a' }] as any[];
+            const spy = vi.spyOn(api, 'fetchFontsByIds').mockResolvedValueOnce(fonts1);
+
+            const store = new BatchFontStore(['a']);
+            await vi.waitFor(() => expect(store.fonts).toEqual(fonts1), { timeout: 1000 });
+
+            spy.mockClear();
+            store.setIds([]);
+
+            await vi.waitFor(() => expect(store.fonts).toEqual([]), { timeout: 1000 });
+            expect(spy).not.toHaveBeenCalled();
         });
     });
 

src/shared/api/queryKeys.test.ts

@@ -27,6 +27,17 @@ describe('fontKeys', () => {
         it('should handle empty ID arrays', () => {
             expect(fontKeys.batch([])).toEqual(['fonts', 'batch', []]);
         });
+
+        it('should not mutate the input array when sorting', () => {
+            const ids = ['c', 'b', 'a'];
+            fontKeys.batch(ids);
+            expect(ids).toEqual(['c', 'b', 'a']);
+        });
+
+        it('batch key should be rooted in batches() base', () => {
+            const key = fontKeys.batch(['a']);
+            expect(key.slice(0, 2)).toEqual(fontKeys.batches());
+        });
     });
 
     describe('List Keys (Parameters)', () => {
@@ -38,11 +49,25 @@ describe('fontKeys', () => {
         it('should handle empty parameters', () => {
             expect(fontKeys.list({})).toEqual(['fonts', 'list', {}]);
         });
+
+        it('list key should be rooted in lists() base', () => {
+            const key = fontKeys.list({ provider: 'google' });
+            expect(key.slice(0, 2)).toEqual(fontKeys.lists());
+        });
     });
 
     describe('Detail Keys', () => {
         it('should generate unique detail keys per ID', () => {
             expect(fontKeys.detail('roboto')).toEqual(['fonts', 'detail', 'roboto']);
         });
+
+        it('should generate different keys for different IDs', () => {
+            expect(fontKeys.detail('roboto')).not.toEqual(fontKeys.detail('open-sans'));
+        });
+
+        it('detail key should be rooted in details() base', () => {
+            const key = fontKeys.detail('roboto');
+            expect(key.slice(0, 2)).toEqual(fontKeys.details());
+        });
     });
 });

src/shared/lib/helpers/BaseQueryStore.test.ts

@@ -51,6 +51,12 @@ describe('BaseQueryStore', () => {
             await vi.waitFor(() => expect(store.data).toBe('ok'), { timeout: 1000 });
             expect(store.isLoading).toBe(false);
         });
+
+        it('should have undefined data and no error in initial loading state', () => {
+            const store = new TestStore(['initial-state'], () => new Promise(r => setTimeout(() => r('late'), 500)));
+            expect(store.data).toBeUndefined();
+            expect(store.isError).toBe(false);
+        });
     });
 
     describe('Error Handling', () => {