diff --git a/packages/root/src/core/hooks/useAssetMap.test.tsx b/packages/root/src/core/hooks/useAssetMap.test.tsx
new file mode 100644
index 00000000..7b7f62fd
--- /dev/null
+++ b/packages/root/src/core/hooks/useAssetMap.test.tsx
@@ -0,0 +1,120 @@
+import {renderToString} from 'preact-render-to-string';
+import {expect, test} from 'vitest';
+import {renderJsxToString} from '../../jsx/jsx-render.js';
+import type {Asset, AssetMap} from '../../render/asset-map/asset-map.js';
+import {
+  ASSET_MAP_CONTEXT,
+  useAsset,
+  useAssetMap,
+  useAssetUrl,
+} from './useAssetMap.js';
+
+/**
+ * Returns a stub asset map backed by a `src` -> `assetUrl` mapping, mimicking
+ * the lookups performed by `BuildAssetMap` and `DevServerAssetMap`.
+ */
+function testAssetMap(assetUrls: Record<string, string>): AssetMap {
+  return {
+    get: (src: string): Asset | null => {
+      if (!(src in assetUrls)) {
+        return null;
+      }
+      return {
+        src: src,
+        assetUrl: assetUrls[src],
+        getCssDeps: async () => [],
+        getJsDeps: async () => [],
+        getModulePreloadDeps: async () => [],
+      };
+    },
+  };
+}
+
+const assetMap = testAssetMap({
+  'bundles/main.ts': '/assets/main.abcd1234.js',
+  // Route files are in the manifest for their CSS deps, but have no asset URL.
+  'routes/index.tsx': '',
+});
+
+/**
+ * The renderer picks between `preact-render-to-string` and `@blinkk/root/jsx`
+ * depending on the `jsxRenderer` config, so the hook is verified against both.
+ */
+const renderers: Array<[string, (vnode: any) => string]> = [
+  ['preact-render-to-string', (vnode) => renderToString(vnode)],
+  ['@blinkk/root/jsx', (vnode) => renderJsxToString(vnode, {mode: 'minimal'})],
+];
+
+/** Renders a component with the asset map provided by the renderer. */
+function render(
+  vnode: any,
+  options?: {assetMap?: AssetMap; renderJsx?: (vnode: any) => string}
+) {
+  const renderJsx = options?.renderJsx || renderers[0][1];
+  if (!options?.assetMap) {
+    return renderJsx(vnode);
+  }
+  return renderJsx(
+    <ASSET_MAP_CONTEXT.Provider value={options.assetMap}>
+      {vnode}
+    </ASSET_MAP_CONTEXT.Provider>
+  );
+}
+
+test.each(renderers)(
+  'useAssetUrl() returns the compiled asset url (%s)',
+  (_name, renderJsx) => {
+    function Page() {
+      return <div data-main={useAssetUrl('bundles/main.ts')} />;
+    }
+    expect(render(<Page />, {assetMap, renderJsx})).toBe(
+      '<div data-main="/assets/main.abcd1234.js"></div>'
+    );
+  }
+);
+
+test('useAssetUrl() accepts a leading slash', () => {
+  function Page() {
+    return <div data-main={useAssetUrl('/bundles/main.ts')} />;
+  }
+  expect(render(<Page />, {assetMap})).toBe(
+    '<div data-main="/assets/main.abcd1234.js"></div>'
+  );
+});
+
+test('useAssetUrl() throws when the src is not in the asset map', () => {
+  function Page() {
+    return <div data-main={useAssetUrl('/bundles/missing.ts')} />;
+  }
+  expect(() => render(<Page />, {assetMap})).toThrow(
+    'asset not found: /bundles/missing.ts'
+  );
+});
+
+test('useAssetUrl() throws when the asset has no serving url', () => {
+  function Page() {
+    return <div data-main={useAssetUrl('routes/index.tsx')} />;
+  }
+  expect(() => render(<Page />, {assetMap})).toThrow(
+    'asset not found: routes/index.tsx'
+  );
+});
+
+test('useAsset() returns the asset from the module graph', () => {
+  let asset: Asset | null = null;
+  function Page() {
+    asset = useAsset('/bundles/main.ts');
+    return <div />;
+  }
+  render(<Page />, {assetMap});
+  expect(asset!.src).toBe('bundles/main.ts');
+  expect(asset!.assetUrl).toBe('/assets/main.abcd1234.js');
+});
+
+test('useAssetMap() throws when rendered outside of the provider', () => {
+  function Page() {
+    useAssetMap();
+    return <div />;
+  }
+  expect(() => render(<Page />)).toThrow('ASSET_MAP_CONTEXT not found');
+});
diff --git a/packages/root/src/render/asset-map/dev-asset-map.test.ts b/packages/root/src/render/asset-map/dev-asset-map.test.ts
new file mode 100644
index 00000000..907d82f5
--- /dev/null
+++ b/packages/root/src/render/asset-map/dev-asset-map.test.ts
@@ -0,0 +1,70 @@
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import type {ModuleGraph} from 'vite';
+import {afterEach, beforeEach, expect, test, vi} from 'vitest';
+import {RootConfig} from '../../core/config.js';
+import {DevServerAssetMap} from './dev-asset-map.js';
+
+let workspaceDir: string;
+let rootDir: string;
+let assetMap: DevServerAssetMap;
+
+// A module graph that never resolves a file, which exercises the fallback
+// branches that serve files that never made it into vite's module graph.
+const emptyModuleGraph = {
+  getModulesByFile: () => undefined,
+} as unknown as ModuleGraph;
+
+beforeEach(() => {
+  workspaceDir = fs.mkdtempSync(path.join(os.tmpdir(), 'root-dev-assets-'));
+  // `searchForWorkspaceRoot()` walks up for a `pnpm-workspace.yaml`, so the
+  // workspace root is deterministic within the temp dir.
+  fs.writeFileSync(path.join(workspaceDir, 'pnpm-workspace.yaml'), '');
+  rootDir = path.join(workspaceDir, 'site');
+  fs.mkdirSync(rootDir);
+  assetMap = new DevServerAssetMap({rootDir} as RootConfig, emptyModuleGraph);
+});
+
+afterEach(() => {
+  if (workspaceDir) {
+    fs.rmSync(workspaceDir, {recursive: true, force: true});
+  }
+});
+
+test('serves files within the project from the root dir', () => {
+  const asset = assetMap.get('bundles/main.ts');
+  expect(asset!.assetUrl).toBe('/bundles/main.ts');
+});
+
+test('serves sibling dirs sharing the root dir prefix from /@fs/', () => {
+  // `<workspace>/site-legacy` is a sibling of `<workspace>/site`, not a child
+  // of it, even though its path starts with the root dir's path.
+  const filePath = path.join(workspaceDir, 'site-legacy/main.ts');
+  fs.mkdirSync(path.dirname(filePath));
+  fs.writeFileSync(filePath, 'export default 1;\n');
+
+  const asset = assetMap.get('../site-legacy/main.ts');
+  expect(asset!.assetUrl).toBe(`/@fs/${filePath}`);
+});
+
+test('serves workspace files that do not exist on disk', () => {
+  const filePath = path.join(workspaceDir, 'packages/ui/main.ts');
+  const asset = assetMap.get('../packages/ui/main.ts');
+  expect(asset!.assetUrl).toBe(`/@fs/${filePath}`);
+});
+
+test('returns null for files outside of the workspace', () => {
+  // The missing-asset lookup logs via console.log; stub it so the test output
+  // stays clean, and assert it fired.
+  const logSpy = vi.spyOn(console, 'log').mockImplementation(() => {});
+  try {
+    const src = path.relative(rootDir, path.join(os.tmpdir(), 'outside.ts'));
+    expect(assetMap.get(src)).toBeNull();
+    expect(logSpy).toHaveBeenCalledWith(
+      `could not find asset in asset map: ${src}`
+    );
+  } finally {
+    logSpy.mockRestore();
+  }
+});