Allow optional Street Level provider composition

src/app/layers/streetLevel.test.mjs

@@ -0,0 +1,29 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { createApplicationStreetLevel } from './streetLevel.js';
+import { fakeStreetLevelProvider } from '../../testSupport/streetLevelFakes.mjs';
+
+test('explicit providers replace the default source and an empty list removes it', () => {
+  const sources = { mapillary: {} };
+  const provider = fakeStreetLevelProvider({
+    id: 'example',
+    pickPrefix: 'example:',
+  });
+  const layer = createApplicationStreetLevel({
+    sources,
+    providers: [provider],
+  });
+  assert.deepEqual(layer.providerIds, ['example']);
+  assert.deepEqual(
+    createApplicationStreetLevel({ sources, providers: [] }).providerIds,
+    [],
+  );
+  assert.throws(
+    () => createApplicationStreetLevel({ sources }),
+    /Mapillary source/,
+  );
+  assert.throws(
+    () => createApplicationStreetLevel({ providers: null }),
+    /array/,
+  );
+});