test(ui): add UserButton connected integration test

.changeset/mosaic-user-button-action-feedback.md

@@ -0,0 +1,2 @@
+---
+---

packages/ui/src/mosaic/hooks/__tests__/useSpinDelay.test.ts

@@ -76,6 +76,27 @@ describe('useSpinDelay', () => {
     expect(result.current).toBeNull();
   });
 
+  // Direct feedback on a click has nothing to debounce, so a zero delay must not cost a timer's
+  // worth of render passes before the spinner appears.
+  it('surfaces the value in the same pass when there is no delay to wait out', async () => {
+    const { result, rerender } = render(null, { delay: 0, minDuration: 200 });
+    await act(() => rerender({ value: 'a' }));
+
+    expect(result.current).toBe('a');
+  });
+
+  it('still holds a zero-delay value for minDuration', async () => {
+    const { result, rerender } = render(null, { delay: 0, minDuration: 200 });
+    await act(() => rerender({ value: 'a' }));
+    await act(() => rerender({ value: null }));
+
+    await advance(199);
+    expect(result.current).toBe('a');
+
+    await advance(1);
+    expect(result.current).toBeNull();
+  });
+
   it('swaps to a new value immediately when one replaces another mid-show', async () => {
     const { result, rerender } = render(null, { delay: 500, minDuration: 200 });
     await act(() => rerender({ value: 'a' }));

packages/ui/src/mosaic/hooks/useSpinDelay.ts

@@ -1,7 +1,7 @@
 import { useEffect, useRef, useState } from 'react';
 
 export interface SpinDelayOptions {
-  /** Wait this long before showing the value, so quick actions never flash a spinner. */
+  /** Wait this long before showing the value, so quick actions never flash a spinner. `0` shows it straight away. */
   delay?: number;
   /** Once shown, keep the value up at least this long, so the spinner never flickers off. */
   minDuration?: number;
@@ -25,11 +25,17 @@ export function useSpinDelay<T>(value: T | null, options: SpinDelayOptions = {})
   const shownAt = useRef(0);
 
   useEffect(() => {
-    // Nothing showing yet: arm a timer so the value only surfaces if it outlasts `delay`.
+    // Nothing showing yet: arm a timer so the value only surfaces if it outlasts `delay`. With no
+    // delay there is nothing to outlast, so it surfaces in this pass rather than a timer's.
     if (shown === null) {
       if (value === null) {
         return;
       }
+      if (delay <= 0) {
+        shownAt.current = Date.now();
+        setShown(value);
+        return;
+      }
       const timer = setTimeout(() => {
         shownAt.current = Date.now();
         setShown(value);