these too

frontend/src/lib/api.test.ts

@@ -0,0 +1,67 @@
+import { describe, expect, it } from 'vitest';
+
+import type { FeatureMeta } from '../types';
+import { apiUrl, assertOk, buildFilterString, isAbortError } from './api';
+
+describe('api utilities', () => {
+  it('builds API URLs from endpoint names, paths, and params', () => {
+    expect(apiUrl('features')).toBe('/api/features');
+    expect(apiUrl('/custom/path')).toBe('/custom/path');
+    expect(apiUrl('hexagons', new URLSearchParams({ bounds: '1,2,3,4' }))).toBe(
+      '/api/hexagons?bounds=1%2C2%2C3%2C4'
+    );
+  });
+
+  it('throws helpful errors for non-OK responses', () => {
+    expect(() => assertOk(new Response(null, { status: 204 }), 'empty')).not.toThrow();
+    expect(() =>
+      assertOk(new Response(null, { status: 404, statusText: 'Not Found' }), 'lookup')
+    ).toThrow('lookup: HTTP 404 Not Found');
+  });
+
+  it('recognizes AbortError instances', () => {
+    const abort = new Error('Aborted');
+    abort.name = 'AbortError';
+    const regular = new Error('nope');
+
+    expect(isAbortError(abort)).toBe(true);
+    expect(isAbortError(regular)).toBe(false);
+  });
+
+  it('serializes numeric, absolute, and enum filters for backend routes', () => {
+    const features: FeatureMeta[] = [
+      { name: 'Last known price', type: 'numeric', min: 0, max: 1_000_000 },
+      {
+        name: 'Estimated current price',
+        type: 'numeric',
+        absolute: true,
+        histogram: { min: 0, max: 2_000_000, p1: 0, p99: 2_000_000, counts: [1] },
+      },
+      { name: 'Property type', type: 'enum', values: ['Flat', 'House'] },
+    ];
+
+    expect(
+      buildFilterString(
+        {
+          'Last known price': [100_000, 500_000],
+          'Estimated current price': [0, 2_000_000],
+          'Property type': ['Flat', 'House'],
+        },
+        features
+      )
+    ).toBe(
+      'Last known price:100000:500000;;Estimated current price:0:inf;;Property type:Flat|House'
+    );
+
+    expect(
+      buildFilterString(
+        {
+          'Last known price': [100_000, 500_000],
+          'Property type': ['Flat'],
+        },
+        features,
+        'Last known price'
+      )
+    ).toBe('Property type:Flat');
+  });
+});