diff --git a/quartz/util/url.test.ts b/quartz/util/url.test.ts
new file mode 100644
index 000000000..15d7e1263
--- /dev/null
+++ b/quartz/util/url.test.ts
@@ -0,0 +1,29 @@
+import { describe, it } from "node:test"
+import { getExtFromUrl } from "./url"
+import assert from "node:assert/strict"
+
+describe("getExtFromUrl", () => {
+  it("should return the correct file extension from a URL", () => {
+    const url = "https://example.com/image.jpg"
+    const ext = getExtFromUrl(url)
+    assert.strictEqual(ext, ".jpg")
+  })
+
+  it("should return undefined for URLs without an extension", () => {
+    const url = "https://example.com/image"
+    const ext = getExtFromUrl(url)
+    assert.strictEqual(ext, undefined)
+  })
+
+  it("should handle URLs with query parameters", () => {
+    const url = "https://example.com/image.jpg?size=large"
+    const ext = getExtFromUrl(url)
+    assert.strictEqual(ext, ".jpg")
+  })
+
+  it("should handle URLs with hash fragments", () => {
+    const url = "https://example.com/image.jpg#section1"
+    const ext = getExtFromUrl(url)
+    assert.strictEqual(ext, ".jpg")
+  })
+})