diff --git a/lib/auth/__tests__/guard.test.ts b/lib/auth/__tests__/guard.test.ts
new file mode 100644
index 0000000..5d21a7b
--- /dev/null
+++ b/lib/auth/__tests__/guard.test.ts
@@ -0,0 +1,165 @@
+import { describe, it, expect, vi, beforeEach, beforeAll } from "vitest"
+
+// Mock the auth module — no real betterAuth initialisation should run.
+vi.mock("@/lib/auth", () => ({
+  auth: {
+    api: {
+      getSession: vi.fn(),
+    },
+  },
+}))
+
+// Use dynamic imports so vi.mock is guaranteed to be registered before
+// any module evaluation in bun test's shared-module-cache multi-file mode.
+let requireAuth: typeof import("../guard")["requireAuth"]
+let requireRole: typeof import("../guard")["requireRole"]
+let requireAdmin: typeof import("../guard")["requireAdmin"]
+let requireContributorOrAdmin: typeof import("../guard")["requireContributorOrAdmin"]
+let requireModeratorOrAdmin: typeof import("../guard")["requireModeratorOrAdmin"]
+let getSession: ReturnType<typeof vi.fn>
+
+beforeAll(async () => {
+  const guard = await import("../guard")
+  requireAuth = guard.requireAuth
+  requireRole = guard.requireRole
+  requireAdmin = guard.requireAdmin
+  requireContributorOrAdmin = guard.requireContributorOrAdmin
+  requireModeratorOrAdmin = guard.requireModeratorOrAdmin
+
+  const mocked = await import("@/lib/auth")
+  getSession = mocked.auth.api.getSession
+})
+
+function mockSession(overrides: Record<string, unknown> = {}) {
+  getSession.mockResolvedValue({
+    user: {
+      id: "user-1",
+      name: "Test User",
+      email: "test@example.com",
+      role: "user",
+      ...overrides,
+    },
+    session: {
+      id: "session-1",
+      userId: "user-1",
+      token: "token-abc",
+    },
+  })
+}
+
+function mockNoSession() {
+  getSession.mockResolvedValue(null)
+}
+
+beforeEach(() => {
+  getSession.mockReset()
+})
+
+describe("requireAuth", () => {
+  it("returns ok with user and session when authenticated", async () => {
+    mockSession()
+    const result = await requireAuth(new Headers())
+    expect(result.ok).toBe(true)
+    if (result.ok) {
+      expect(result.user.id).toBe("user-1")
+      expect(result.session.id).toBe("session-1")
+    }
+  })
+
+  it("returns error 401 when not authenticated", async () => {
+    mockNoSession()
+    const result = await requireAuth(new Headers())
+    expect(result.ok).toBe(false)
+    if (!result.ok) {
+      expect(result.status).toBe(401)
+      expect(result.error).toBe("Unauthorized")
+    }
+  })
+})
+
+describe("requireRole", () => {
+  it("allows user with matching role", async () => {
+    mockSession({ role: "admin" })
+    const result = await requireRole(new Headers(), ["admin"])
+    expect(result.ok).toBe(true)
+  })
+
+  it("denies user with non-matching role (403)", async () => {
+    mockSession({ role: "user" })
+    const result = await requireRole(new Headers(), ["admin"])
+    expect(result.ok).toBe(false)
+    if (!result.ok) {
+      expect(result.status).toBe(403)
+      expect(result.error).toBe("Forbidden")
+    }
+  })
+
+  it("returns 401 when not authenticated", async () => {
+    mockNoSession()
+    const result = await requireRole(new Headers(), ["admin"])
+    expect(result.ok).toBe(false)
+    if (!result.ok) {
+      expect(result.status).toBe(401)
+    }
+  })
+
+  it("defaults to 'user' role when role is null", async () => {
+    mockSession({ role: null })
+    const result = await requireRole(new Headers(), ["user"])
+    expect(result.ok).toBe(true)
+  })
+})
+
+describe("requireAdmin", () => {
+  it("allows admin user", async () => {
+    mockSession({ role: "admin" })
+    const result = await requireAdmin(new Headers())
+    expect(result.ok).toBe(true)
+  })
+
+  it("denies non-admin user (403)", async () => {
+    mockSession({ role: "moderator" })
+    const result = await requireAdmin(new Headers())
+    expect(result.ok).toBe(false)
+  })
+})
+
+describe("requireContributorOrAdmin", () => {
+  it("allows contributor", async () => {
+    mockSession({ role: "contributor" })
+    const result = await requireContributorOrAdmin(new Headers())
+    expect(result.ok).toBe(true)
+  })
+
+  it("allows admin", async () => {
+    mockSession({ role: "admin" })
+    const result = await requireContributorOrAdmin(new Headers())
+    expect(result.ok).toBe(true)
+  })
+
+  it("denies regular user", async () => {
+    mockSession({ role: "user" })
+    const result = await requireContributorOrAdmin(new Headers())
+    expect(result.ok).toBe(false)
+  })
+})
+
+describe("requireModeratorOrAdmin", () => {
+  it("allows moderator", async () => {
+    mockSession({ role: "moderator" })
+    const result = await requireModeratorOrAdmin(new Headers())
+    expect(result.ok).toBe(true)
+  })
+
+  it("allows admin", async () => {
+    mockSession({ role: "admin" })
+    const result = await requireModeratorOrAdmin(new Headers())
+    expect(result.ok).toBe(true)
+  })
+
+  it("denies contributor", async () => {
+    mockSession({ role: "contributor" })
+    const result = await requireModeratorOrAdmin(new Headers())
+    expect(result.ok).toBe(false)
+  })
+})
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