Add a test for @salsakran

frontend/test/unit/lib/dom.spec.js

+import { getSelectionPosition, setSelectionPosition } from "metabase/lib/dom"
+
+describe("getSelectionPosition/setSelectionPosition", () => {
+    let container;
+    beforeEach(() => {
+        container = document.createElement("div");
+        document.body.appendChild(container);
+    })
+    afterEach(() => {
+        document.body.removeChild(container);
+    })
+
+    it("should get/set selection on input correctly", () => {
+        let input = document.createElement("input");
+        container.appendChild(input);
+        input.value = "hello world";
+        setSelectionPosition(input, [3, 6]);
+        const position = getSelectionPosition(input);
+        expect(position).toEqual([3, 6]);
+    });
+    it("should get/set selection on contenteditable correctly", () => {
+        let contenteditable = document.createElement("div");
+        container.appendChild(contenteditable);
+        contenteditable.textContent = "<div>hello world</div>"
+        setSelectionPosition(contenteditable, [3, 6]);
+        const position = getSelectionPosition(contenteditable);
+        expect(position).toEqual([3, 6]);
+    });
+})