node:inspector + V8 Profiler.*PreciseCoverage

. index.mjs

import { writeFileSync } from "node:fs";
import inspector from "node:inspector";

function firstMethod() {}
function secondMethod() {}

const session = new inspector.Session();
const collectedCoverage = [];

session.connect();
session.post("Profiler.enable");
session.post("Runtime.enable");
session.post("Profiler.startPreciseCoverage", {
  callCount: true,
  detailed: true,
});

firstMethod();
await collectCoverage();

secondMethod();
await collectCoverage();

async function collectCoverage() {
  await new Promise((resolve, reject) => {
    session.post("Profiler.takePreciseCoverage", async (error, coverage) => {
      if (error) return reject(error);

      const filtered = coverage.result.filter(
        (entry) => !entry.url.startsWith("node:")
      );

      collectedCoverage.push(...filtered);

      resolve();
    });
  });
}

writeFileSync(
  "./coverage.json",
  JSON.stringify(collectedCoverage, null, 2),
  "utf8"
);

coverage.json

[
  {
    "scriptId": "132",
    "url": "file:///x/y/repro/index.mjs",
    "functions": [
      {
        "functionName": "firstMethod",
        "ranges": [
          {
            "startOffset": 82,
            "endOffset": 107,
            "count": 1
          }
        ],
        "isBlockCoverage": true
      },
      {
        "functionName": "collectCoverage",
        "ranges": [
          {
            "startOffset": 465,
            "endOffset": 844,
            "count": 1
          },
          {
            "startOffset": 842,
            "endOffset": 843,
            "count": 0
          }
        ],
        "isBlockCoverage": true
      },
      {
        "functionName": "",
        "ranges": [
          {
            "startOffset": 520,
            "endOffset": 840,
            "count": 1
          }
        ],
        "isBlockCoverage": true
      },
      {
        "functionName": "",
        "ranges": [
          {
            "startOffset": 592,
            "endOffset": 834,
            "count": 0
          }
        ],
        "isBlockCoverage": false
      }
    ]
  },
  {
    "scriptId": "132",
    "url": "file:///x/y/repro/index.mjs",
    "functions": [
      {
        "functionName": "",
        "ranges": [
          {
            "startOffset": 0,
            "endOffset": 940,
            "count": 1
          }
        ],
        "isBlockCoverage": false
      },
      {
        "functionName": "firstMethod",
        "ranges": [
          {
            "startOffset": 82,
            "endOffset": 107,
            "count": 0
          }
        ],
        "isBlockCoverage": true
      },
      {
        "functionName": "secondMethod",
        "ranges": [
          {
            "startOffset": 108,
            "endOffset": 134,
            "count": 1
          }
        ],
        "isBlockCoverage": true
      },
      {
        "functionName": "collectCoverage",
        "ranges": [
          {
            "startOffset": 465,
            "endOffset": 844,
            "count": 1
          }
        ],
        "isBlockCoverage": true
      },
      {
        "functionName": "",
        "ranges": [
          {
            "startOffset": 520,
            "endOffset": 840,
            "count": 1
          }
        ],
        "isBlockCoverage": true
      },
      {
        "functionName": "",
        "ranges": [
          {
            "startOffset": 592,
            "endOffset": 834,
            "count": 1
          },
          {
            "startOffset": 638,
            "endOffset": 659,
            "count": 0
          }
        ],
        "isBlockCoverage": true
      },
      {
        "functionName": "",
        "ranges": [
          {
            "startOffset": 716,
            "endOffset": 757,
            "count": 3
          }
        ],
        "isBlockCoverage": true
      }
    ]
  }
]