tech-log-frontend/tests/unit/v8-coverage-counter-semantics.test.ts

import { execFile } from "node:child_process";
import {
  access,
  mkdtemp,
  readFile,
  rm,
} from "node:fs/promises";
import { tmpdir } from "node:os";
import path from "node:path";
import { promisify } from "node:util";

import { afterEach, describe, expect, it } from "vitest";

import {
  assertV8CoverageCounterSemantics,
  checkV8CoverageCounterSemantics,
} from "../../scripts/lib/v8-coverage-counter-semantics.ts";

const roots: string[] = [];
const execFileAsync = promisify(execFile);
const zeroCounter = Object.freeze({
  total: 0,
  covered: 0,
  skipped: 0,
  pct: 100,
});
const zeroMetrics = Object.freeze({
  lines: zeroCounter,
  statements: zeroCounter,
  functions: zeroCounter,
  branches: zeroCounter,
});
const counterlessPaths = Object.freeze([
  "src/import-empty.ts",
  "src/import-side-effect.ts",
  "src/import-type-empty.ts",
  "src/import-value.ts",
  "src/reexport-named.ts",
  "src/reexport-star.ts",
  "src/type-only.ts",
]);

function fixtureSummary(root: string): Record<string, unknown> {
  return Object.fromEntries([
    [
      "total",
      {
        lines: { total: 1, covered: 1, skipped: 0, pct: 100 },
        statements: { total: 1, covered: 1, skipped: 0, pct: 100 },
        functions: zeroCounter,
        branches: zeroCounter,
      },
    ],
    [
      path.join(root, "src/runtime.ts"),
      {
        lines: { total: 1, covered: 1, skipped: 0, pct: 100 },
        statements: { total: 1, covered: 1, skipped: 0, pct: 100 },
        functions: zeroCounter,
        branches: zeroCounter,
      },
    ],
    ...counterlessPaths.map((modulePath) => [path.join(root, modulePath), zeroMetrics]),
  ]);
}

async function captureFailure(operation: Promise<unknown>): Promise<Error> {
  try {
    await operation;
  } catch (error) {
    if (error instanceof Error) return error;
    throw error;
  }
  throw new Error("expected operation to fail");
}

afterEach(async () => {
  await Promise.all(
    roots.splice(0).map((root) => rm(root, { recursive: true, force: true })),
  );
});

describe("V8 coverage counter semantics", () => {
  it("accepts one counter-bearing row and seven exact counterless rows", () => {
    const root = "/owned-fixture";

    expect(assertV8CoverageCounterSemantics(fixtureSummary(root), root)).toEqual({
      counterBearingModules: ["src/runtime.ts"],
      counterlessModules: counterlessPaths,
    });
  });

  it("rejects a missing or additional producer row", () => {
    const root = "/owned-fixture";
    const missing = fixtureSummary(root);
    delete missing[path.join(root, "src/import-empty.ts")];
    expect(() => assertV8CoverageCounterSemantics(missing, root)).toThrow(
      /row set.*missing.*import-empty/u,
    );

    const additional = fixtureSummary(root);
    additional[path.join(root, "src/unexpected.ts")] = zeroMetrics;
    expect(() => assertV8CoverageCounterSemantics(additional, root)).toThrow(
      /row set.*additional.*unexpected/u,
    );
  });

  it("rejects counterless nonzero and runtime all-zero drift", () => {
    const root = "/owned-fixture";
    const counterlessDrift = fixtureSummary(root);
    counterlessDrift[path.join(root, "src/import-value.ts")] = {
      ...zeroMetrics,
      lines: { total: 1, covered: 1, skipped: 0, pct: 100 },
    };
    expect(() =>
      assertV8CoverageCounterSemantics(counterlessDrift, root),
    ).toThrow(/counterless.*exact all-zero.*import-value/u);

    const runtimeDrift = fixtureSummary(root);
    runtimeDrift[path.join(root, "src/runtime.ts")] = zeroMetrics;
    expect(() => assertV8CoverageCounterSemantics(runtimeDrift, root)).toThrow(
      /runtime.*counter-bearing/u,
    );
  });

  it("rejects producer percentages that do not exactly match their counts", () => {
    const root = "/owned-fixture";
    const totalDrift = fixtureSummary(root);
    totalDrift["total"] = {
      ...totalDrift["total"] as Record<string, unknown>,
      lines: { total: 1, covered: 1, skipped: 0, pct: -500 },
    };
    expect(() => assertV8CoverageCounterSemantics(totalDrift, root)).toThrow(
      /total\.lines.*invalid coverage counters/u,
    );

    const runtimeDrift = fixtureSummary(root);
    runtimeDrift[path.join(root, "src/runtime.ts")] = {
      ...runtimeDrift[path.join(root, "src/runtime.ts")] as Record<
        string,
        unknown
      >,
      lines: { total: 1, covered: 1, skipped: 0, pct: 99.99 },
    };
    expect(() => assertV8CoverageCounterSemantics(runtimeDrift, root)).toThrow(
      /runtime.*lines.*invalid coverage counters/u,
    );
  });

  it("bounds child diagnostics and cleans its owned root on child exit", async () => {
    const ownedRoot = await mkdtemp(path.join(tmpdir(), "v8-counter-exit-"));
    roots.push(ownedRoot);
    const childFailure = Object.assign(new Error("child exit 1"), {
      stdout: "o".repeat(20_000),
      stderr: "e".repeat(20_000),
    });

    const failure = await captureFailure(
      checkV8CoverageCounterSemantics({
        repositoryRoot: process.cwd(),
        createOwnedRoot: async () => ownedRoot,
        runVitest: async () => Promise.reject(childFailure),
      }),
    );

    expect(failure.message).toMatch(/child Vitest failed/u);
    expect(failure.message).toMatch(/truncated/u);
    expect(failure.message.length).toBeLessThan(5_000);
    await expect(access(ownedRoot)).rejects.toMatchObject({ code: "ENOENT" });
  });

  it("fails closed on a missing summary and cleans its owned root", async () => {
    const ownedRoot = await mkdtemp(path.join(tmpdir(), "v8-counter-summary-"));
    roots.push(ownedRoot);

    await expect(
      checkV8CoverageCounterSemantics({
        repositoryRoot: process.cwd(),
        createOwnedRoot: async () => ownedRoot,
        runVitest: async () => ({ stdout: "", stderr: "" }),
      }),
    ).rejects.toThrow(/coverage summary is missing/u);
    await expect(access(ownedRoot)).rejects.toMatchObject({ code: "ENOENT" });
  });

  it("keeps the child fixture outside main Vitest discovery", async () => {
    const outputRoot = await mkdtemp(path.join(tmpdir(), "v8-counter-list-"));
    roots.push(outputRoot);
    const outputPath = path.join(outputRoot, "listed.json");
    await execFileAsync(
      process.execPath,
      [
        path.join(process.cwd(), "node_modules/vitest/vitest.mjs"),
        "list",
        "tests/fixtures/v8-coverage-counter-semantics",
        "--config",
        path.join(process.cwd(), "vitest.config.ts"),
        "--filesOnly",
        "--passWithNoTests",
        "--json",
        outputPath,
        "--no-color",
      ],
      {
        cwd: process.cwd(),
        encoding: "utf8",
        timeout: 30_000,
        maxBuffer: 256 * 1024,
      },
    );

    expect(JSON.parse(await readFile(outputPath, "utf8"))).toEqual([]);
  });
});