test(web): the diff boundary observer counter lives in its fixture

apps/web/src/components/diffs/DiffFileLoadingBoundary.browser.test.tsx

@@ -3,31 +3,34 @@ import { describe, expect, it, vi } from "vite-plus/test";
 import { render } from "../../../test/render";
 import { DiffFileLoadingBoundary } from "./DiffFileLoadingBoundary";
 
-// Like the real observer, every observe() reports the target's current state; this boundary
-// is always in range.
-class InRangeIntersectionObserver {
-  static observeCount = 0;
-  constructor(readonly callback: IntersectionObserverCallback) {}
-  observe(target: Element) {
-    InRangeIntersectionObserver.observeCount += 1;
-    this.callback(
-      [{ target, isIntersecting: true } as IntersectionObserverEntry],
-      this as unknown as IntersectionObserver,
-    );
-  }
-  unobserve() {}
-  disconnect() {}
-}
-
 function stubIntersectionObserver() {
-  InRangeIntersectionObserver.observeCount = 0;
+  let observeCount = 0;
+  // Like the real observer, every observe() reports the target's current state; this boundary
+  // is always in range.
+  class InRangeIntersectionObserver {
+    constructor(readonly callback: IntersectionObserverCallback) {}
+    observe(target: Element) {
+      observeCount += 1;
+      this.callback(
+        [{ target, isIntersecting: true } as IntersectionObserverEntry],
+        this as unknown as IntersectionObserver,
+      );
+    }
+    unobserve() {}
+    disconnect() {}
+  }
   vi.stubGlobal("IntersectionObserver", InRangeIntersectionObserver);
-  return { [Symbol.dispose]: () => vi.unstubAllGlobals() };
+  return {
+    get observeCount() {
+      return observeCount;
+    },
+    [Symbol.dispose]: () => vi.unstubAllGlobals(),
+  };
 }
 
 describe("DiffFileLoadingBoundary", () => {
   it("observes once and loads once while its parent re-renders with a new load", async () => {
-    using _observer = stubIntersectionObserver();
+    using observer = stubIntersectionObserver();
     const load = vi.fn();
     // DiffPanel hands over a new loadNextFiles whenever any file patch changes.
     await using screen = await render(<DiffFileLoadingBoundary load={() => load()} count={8} />, {
@@ -38,12 +41,12 @@ describe("DiffFileLoadingBoundary", () => {
     await screen.rerender(<DiffFileLoadingBoundary load={() => load()} count={8} />);
 
     await expect.element(screen.getByRole("status", { name: "Loading diff…" })).toBeInTheDocument();
-    expect(InRangeIntersectionObserver.observeCount).toBe(1);
+    expect(observer.observeCount).toBe(1);
     expect(load).toHaveBeenCalledTimes(1);
 
     // A settled batch leaves the boundary in range, so it asks for the next one.
     await screen.rerender(<DiffFileLoadingBoundary load={() => load()} count={4} />);
-    expect(InRangeIntersectionObserver.observeCount).toBe(1);
+    expect(observer.observeCount).toBe(1);
     expect(load).toHaveBeenCalledTimes(2);
   });
 });