diff --git a/tests/caching-tests.js b/tests/caching-tests.js
new file mode 100644
index 0000000..79e0caf
--- /dev/null
+++ b/tests/caching-tests.js
@@ -0,0 +1,72 @@
+import { describe, it } from "node:test";
+import assert from "node:assert";
+
+const BASE_URL = "https://developer.allizom.org/";
+
+describe("redirectPreferredLocale", () => {
+  it("should redirect if preferredlocale is set", async () => {
+    let response = await fetch(new URL("/en-US/docs/Web", BASE_URL));
+    assert.ok(response.url.endsWith("/en-US/docs/Web"), response.url);
+
+    response = await fetch(new URL("/en-US/docs/Web", BASE_URL), {
+      headers: new Headers({
+        cookie: "preferredlocale=fr",
+      }),
+    });
+    assert.ok(response.url.endsWith("/fr/docs/Web"), response.url);
+  });
+
+  it("shouldn't redirect if page doesn't exist in preferred locale", async () => {
+    let response = await fetch(
+      new URL("/en-US/docs/MDN/Kitchensink", BASE_URL)
+    );
+    assert.ok(
+      response.url.endsWith("/en-US/docs/MDN/Kitchensink"),
+      response.url
+    );
+
+    response = await fetch(new URL("/en-US/docs/MDN/Kitchensink", BASE_URL), {
+      headers: new Headers({
+        cookie: "preferredlocale=fr",
+      }),
+    });
+    assert.ok(
+      response.url.endsWith("/en-US/docs/MDN/Kitchensink"),
+      response.url
+    );
+  });
+});
+
+describe("redirectLocale", () => {
+  it("should redirect to preferredlocale", async () => {
+    let response = await fetch(new URL("/", BASE_URL), {
+      headers: new Headers({
+        cookie: "preferredlocale=en-US",
+      }),
+    });
+    assert.ok(response.url.endsWith("/en-US/"), response.url);
+
+    response = await fetch(new URL("/", BASE_URL), {
+      headers: new Headers({
+        cookie: "preferredlocale=fr",
+      }),
+    });
+    assert.ok(response.url.endsWith("/fr/"), response.url);
+  });
+
+  it("should redirect to Accept-Language", async () => {
+    let response = await fetch(new URL("/", BASE_URL), {
+      headers: new Headers({
+        "accept-language": "en-US",
+      }),
+    });
+    assert.ok(response.url.endsWith("/en-US/"), response.url);
+
+    response = await fetch(new URL("/", BASE_URL), {
+      headers: new Headers({
+        "accept-language": "fr",
+      }),
+    });
+    assert.ok(response.url.endsWith("/fr/"), response.url);
+  });
+});