test(expandable-tile): add unit tests

tests/setup-tests.ts

@@ -6,4 +6,41 @@ import "../css/all.css";
 // Mock scrollIntoView since it's not implemented in JSDOM
 Element.prototype.scrollIntoView = vi.fn();
 
+// Mock ResizeObserver since it's not implemented in JSDOM
+class ResizeObserverMock {
+  callback: ResizeObserverCallback;
+  elements: Element[];
+
+  constructor(callback: ResizeObserverCallback) {
+    this.callback = callback;
+    this.elements = [];
+  }
+
+  observe(element: Element) {
+    this.elements.push(element);
+    this.callback(
+      [
+        {
+          target: element,
+          contentRect: { height: 100 } as DOMRectReadOnly,
+          borderBoxSize: [],
+          contentBoxSize: [],
+          devicePixelContentBoxSize: [],
+        },
+      ],
+      this,
+    );
+  }
+
+  unobserve(element: Element) {
+    this.elements = this.elements.filter((el) => el !== element);
+  }
+
+  disconnect() {
+    this.elements = [];
+  }
+}
+
+global.ResizeObserver = ResizeObserverMock;
+
 export const user = userEvent.setup();