diff --git a/lib/api/__tests__/auto-pin.test.ts b/lib/api/__tests__/auto-pin.test.ts
new file mode 100644
index 0000000..9d9e0af
--- /dev/null
+++ b/lib/api/__tests__/auto-pin.test.ts
@@ -0,0 +1,112 @@
+import { describe, it, expect, vi, beforeEach } from "vitest"
+import { db } from "@/lib/db/index"
+import { checkAndAutoPin } from "@/lib/api/auto-pin"
+import { performanceEntries } from "@/lib/db/schema"
+import { eq } from "drizzle-orm"
+
+// Mock the database
+vi.mock("@/lib/db/index", () => ({
+  db: {
+    select: vi.fn(),
+    update: vi.fn(),
+  },
+}))
+
+function setupMockEntry(overrides: {
+  id?: string
+  isPinned?: boolean
+  isRemoved?: boolean
+  upvotes?: number
+  downvotes?: number
+}) {
+  const entry = {
+    id: overrides.id ?? "test-entry-1",
+    isPinned: overrides.isPinned ?? false,
+    isRemoved: overrides.isRemoved ?? false,
+    upvotes: overrides.upvotes ?? 0,
+    downvotes: overrides.downvotes ?? 0,
+  }
+
+  // Mock select chain: .select(...).from(...).where(...).limit(...)
+  const limitMock = vi.fn().mockResolvedValue([entry])
+  const whereMock = vi.fn().mockReturnValue({ limit: limitMock })
+  const fromMock = vi.fn().mockReturnValue({ where: whereMock })
+  const selectMock = vi.fn().mockReturnValue({ from: fromMock })
+  ;(db.select as any).mockReturnValue({ from: fromMock })
+
+  // Mock update chain: .update(...).set(...).where(...)
+  const updateWhereMock = vi.fn().mockResolvedValue(undefined)
+  const updateSetMock = vi.fn().mockReturnValue({ where: updateWhereMock })
+  const updateMock = vi.fn().mockReturnValue({ set: updateSetMock })
+  ;(db.update as any).mockImplementation(updateMock)
+
+  return entry
+}
+
+describe("checkAndAutoPin", () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+  })
+
+  it("pins an entry with 8 upvotes and 2 downvotes (80% approval, 10 total)", async () => {
+    setupMockEntry({ upvotes: 8, downvotes: 2 })
+
+    const result = await checkAndAutoPin("test-entry-1")
+    expect(result).toBe(true)
+  })
+
+  it("does NOT pin an entry with 7 upvotes and 1 downvote (< 8 absolute upvotes)", async () => {
+    setupMockEntry({ upvotes: 7, downvotes: 1 })
+
+    const result = await checkAndAutoPin("test-entry-1")
+    expect(result).toBe(false)
+  })
+
+  it("does NOT pin an entry with 8 upvotes and 0 downvotes (< 10 total votes)", async () => {
+    setupMockEntry({ upvotes: 8, downvotes: 0 })
+
+    const result = await checkAndAutoPin("test-entry-1")
+    expect(result).toBe(false)
+  })
+
+  it("does NOT pin an entry with 6 upvotes and 4 downvotes (60% approval, below 80%)", async () => {
+    setupMockEntry({ upvotes: 6, downvotes: 4 })
+
+    const result = await checkAndAutoPin("test-entry-1")
+    expect(result).toBe(false)
+  })
+
+  it("does NOT pin an already-pinned entry", async () => {
+    setupMockEntry({ isPinned: true, upvotes: 20, downvotes: 0 })
+
+    const result = await checkAndAutoPin("test-entry-1")
+    expect(result).toBe(false)
+  })
+
+  it("does NOT pin a removed entry", async () => {
+    setupMockEntry({ isRemoved: true, upvotes: 20, downvotes: 0 })
+
+    const result = await checkAndAutoPin("test-entry-1")
+    expect(result).toBe(false)
+  })
+
+  it("pins an entry with 20 upvotes and 5 downvotes (80% approval exactly)", async () => {
+    setupMockEntry({ upvotes: 20, downvotes: 5 })
+
+    const result = await checkAndAutoPin("test-entry-1")
+    expect(result).toBe(true)
+  })
+
+  it("does NOT pin when entry is not found", async () => {
+    // Mock select returning empty array
+    const limitMock = vi.fn().mockResolvedValue([])
+    const whereMock = vi.fn().mockReturnValue({ limit: limitMock })
+    const fromMock = vi.fn().mockReturnValue({ where: whereMock })
+    const selectMock = vi.fn().mockReturnValue({ from: fromMock })
+    ;(db.select as any).mockReturnValue({ from: fromMock })
+    ;(db.update as any) = vi.fn()
+
+    const result = await checkAndAutoPin("nonexistent")
+    expect(result).toBe(false)
+  })
+})