tests.duplicate-mock-setup

Flags repeated test mock/setup shapes across several test files.

• Family: tests
• Severity: medium
• Scope: file
• Requires: repo.testMockDuplication

How it works

A repo-level fact fingerprints statement-level mock/setup shapes inside test files. The rule reports a file when one of those shapes appears in 3 or more test files.

Generic labels such as vi.mock, jest.mock, vi.spyOn, jest.spyOn, sinon.stub, and sinon.spy are filtered out so routine framework setup does not dominate the signal. Cleanup-only statements like mockReset and mockClear are also ignored.

Flagged example

// users.test.ts
vi.mocked(api.fetchUser).mockResolvedValue({ id: 1, name: "Ada" });

// teams.test.ts
vi.mocked(api.fetchUser).mockResolvedValue({ id: 2, name: "Lin" });

// accounts.test.ts
vi.mocked(api.fetchUser).mockResolvedValue({ id: 3, name: "Max" });

Once that same setup shape appears in 3 files, each participating file gets a finding.

Usually ignored

vi.mock("./client");
vi.clearAllMocks();

Generic mock declarations and cleanup-only statements do not contribute to this rule.

How to fix / do this better

When the same mock setup keeps reappearing, prefer shared test helpers over repeating the setup inline.

Better options:

• move repeated mock wiring into a factory or fixture helper
• centralize common setup in beforeEach when it is truly shared
• expose small scenario builders so tests vary only the interesting values

function mockUserFetch(overrides: Partial<User> = {}) {
  vi.mocked(api.fetchUser).mockResolvedValue({ id: 1, name: "Ada", ...overrides });
}

That keeps test intent focused on what changes per case instead of duplicating the same mock plumbing in every file.

Scoring

Each duplicate setup cluster adds 1 + 0.5 * (fileCount - 2) for the current file, capped at 5.

Benchmark signal

Small pinned rule benchmark (manifest):

• Signal rank: #9 of 9
• Signal score: 0.63 / 1.00
• Best separating metric: findings / file (0.70)
• Hit rate: 3/6 AI repos vs 1/5 mature OSS repos
• Full results: rule signal report