diff --git a/frontend/src/utils/password_complexity/index.test.ts b/frontend/src/utils/password_complexity/index.test.ts
new file mode 100644
index 000000000..a7fd0799e
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+++ b/frontend/src/utils/password_complexity/index.test.ts
@@ -0,0 +1,52 @@
+// Copyright 2026 Element Creations Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+// Please see LICENSE files in the repository root for full details.
+
+import type { TFunction } from "i18next";
+import { describe, expect, it } from "vitest";
+
+import { estimatePasswordComplexity } from "./index";
+
+// Fake translator that echoes the key back, so we can assert which
+// warning/suggestion strings the estimator produced.
+const t = ((key: string) => key) as unknown as TFunction;
+
+describe("estimatePasswordComplexity()", () => {
+  it("scores a strong password highly", async () => {
+    const result = await estimatePasswordComplexity(
+      "correcthorsebatterystaple",
+      t,
+    );
+    expect(result.score).toBeGreaterThanOrEqual(3);
+  });
+
+  it("scores a common password as the weakest", async () => {
+    const result = await estimatePasswordComplexity("password", t);
+    expect(result.score).toBe(0);
+  });
+
+  it("flags a repeated password", async () => {
+    const result = await estimatePasswordComplexity("aaaaaa", t);
+    expect(result.score).toBe(0);
+    expect(result.improvementsText).toContain(
+      "frontend.password_strength.warning.simple_repeat",
+    );
+  });
+
+  // Regression test for the keyboard adjacency graphs being misloaded.
+  it("detects keyboard-walk patterns via the adjacency graphs", async () => {
+    const result = await estimatePasswordComplexity("fdsapoiuytr", t);
+    expect(result.improvementsText).toContain(
+      "frontend.password_strength.warning.straight_row",
+    );
+    expect(result.improvementsText).toContain(
+      "frontend.password_strength.suggestion.longer_keyboard_pattern",
+    );
+  });
+
+  it("always returns localised score text", async () => {
+    const result = await estimatePasswordComplexity("password", t);
+    expect(result.scoreText).toBe("frontend.password_strength.score.0");
+  });
+});