test_runner: report covered lines, functions and branches to reporters

This is a breaking change for the format of test:coverage events. But
the test coverage is still experimental, so I don't believe it requires
a semver-major bump.

Fixes #49303

PR-URL: #49320
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>

doc/api/test.md

@@ -2026,8 +2026,18 @@ object, streaming a series of events representing the execution of the tests.
       * `coveredLinePercent` {number} The percentage of lines covered.
       * `coveredBranchPercent` {number} The percentage of branches covered.
       * `coveredFunctionPercent` {number} The percentage of functions covered.
-      * `uncoveredLineNumbers` {Array} An array of integers representing line
-        numbers that are uncovered.
+      * `functions` {Array} An array of functions representing function
+        coverage.
+        * `name` {string} The name of the function.
+        * `line` {number} The line number where the function is defined.
+        * `count` {number} The number of times the function was called.
+      * `branches` {Array} An array of branches representing branch coverage.
+        * `line` {number} The line number where the branch is defined.
+        * `count` {number} The number of times the branch was taken.
+      * `lines` {Array} An array of lines representing line
+        numbers and the number of times they were covered.
+        * `line` {number} The line number.
+        * `count` {number} The number of times the line was covered.
     * `totals` {Object} An object containing a summary of coverage for all
       files.
       * `totalLineCount` {number} The total number of lines.

lib/internal/test_runner/coverage.js

@@ -13,6 +13,7 @@ const {
   StringPrototypeIncludes,
   StringPrototypeLocaleCompare,
   StringPrototypeStartsWith,
+  MathMax,
 } = primordials;
 const {
   copyFileSync,
@@ -43,6 +44,7 @@ class CoverageLine {
     this.startOffset = startOffset;
     this.endOffset = startOffset + src.length - newlineLength;
     this.ignore = false;
+    this.count = 0;
     this.#covered = true;
   }
 
@@ -118,6 +120,8 @@ class TestCoverage {
       let totalFunctions = 0;
       let branchesCovered = 0;
       let functionsCovered = 0;
+      const functionReports = [];
+      const branchReports = [];
 
       const lines = ArrayPrototypeMap(linesWithBreaks, (line, i) => {
         const startOffset = offset;
@@ -159,12 +163,20 @@ class TestCoverage {
       for (let j = 0; j < functions.length; ++j) {
         const { isBlockCoverage, ranges } = functions[j];
 
+        let maxCountPerFunction = 0;
         for (let k = 0; k < ranges.length; ++k) {
           const range = ranges[k];
+          maxCountPerFunction = MathMax(maxCountPerFunction, range.count);
 
           mapRangeToLines(range, lines);
 
           if (isBlockCoverage) {
+            ArrayPrototypePush(branchReports, {
+              __proto__: null,
+              line: range.lines[0].line,
+              count: range.count,
+            });
+
             if (range.count !== 0 ||
                 range.ignoredLines === range.lines.length) {
               branchesCovered++;
@@ -177,6 +189,13 @@ class TestCoverage {
         if (j > 0 && ranges.length > 0) {
           const range = ranges[0];
 
+          ArrayPrototypePush(functionReports, {
+            __proto__: null,
+            name: functions[j].functionName,
+            count: maxCountPerFunction,
+            line: range.lines[0].line,
+          });
+
           if (range.count !== 0 || range.ignoredLines === range.lines.length) {
             functionsCovered++;
           }
@@ -186,15 +205,19 @@ class TestCoverage {
       }
 
       let coveredCnt = 0;
-      const uncoveredLineNums = [];
+      const lineReports = [];
 
       for (let j = 0; j < lines.length; ++j) {
         const line = lines[j];
-
+        if (!line.ignore) {
+          ArrayPrototypePush(lineReports, {
+            __proto__: null,
+            line: line.line,
+            count: line.count,
+          });
+        }
         if (line.covered || line.ignore) {
           coveredCnt++;
-        } else {
-          ArrayPrototypePush(uncoveredLineNums, line.line);
         }
       }
 
@@ -210,7 +233,9 @@ class TestCoverage {
         coveredLinePercent: toPercentage(coveredCnt, lines.length),
         coveredBranchPercent: toPercentage(branchesCovered, totalBranches),
         coveredFunctionPercent: toPercentage(functionsCovered, totalFunctions),
-        uncoveredLineNumbers: uncoveredLineNums,
+        functions: functionReports,
+        branches: branchReports,
+        lines: lineReports,
       });
 
       coverageSummary.totals.totalLineCount += lines.length;
@@ -320,6 +345,11 @@ function mapRangeToLines(range, lines) {
         if (count === 0 && startOffset <= line.startOffset &&
             endOffset >= line.endOffset) {
           line.covered = false;
+          line.count = 0;
+        }
+        if (count > 0 && startOffset <= line.startOffset &&
+            endOffset >= line.endOffset) {
+          line.count = count;
         }
 
         ArrayPrototypePush(mappedLines, line);

lib/internal/test_runner/utils.js

@@ -2,6 +2,7 @@
 const {
   ArrayPrototypeJoin,
   ArrayPrototypeMap,
+  ArrayPrototypeFlatMap,
   ArrayPrototypePush,
   ArrayPrototypeReduce,
   ObjectGetOwnPropertyDescriptor,
@@ -303,6 +304,10 @@ function formatLinesToRanges(values) {
   }, []), (range) => ArrayPrototypeJoin(range, '-'));
 }
 
+function getUncoveredLines(lines) {
+  return ArrayPrototypeFlatMap(lines, (line) => (line.count === 0 ? line.line : []));
+}
+
 function formatUncoveredLines(lines, table) {
   if (table) return ArrayPrototypeJoin(formatLinesToRanges(lines), ' ');
   return ArrayPrototypeJoin(lines, ', ');
@@ -332,7 +337,7 @@ function getCoverageReport(pad, summary, symbol, color, table) {
     const columnsWidth = ArrayPrototypeReduce(columnPadLengths, (acc, columnPadLength) => acc + columnPadLength + 3, 0);
 
     uncoveredLinesPadLength = table && ArrayPrototypeReduce(summary.files, (acc, file) =>
-      MathMax(acc, formatUncoveredLines(file.uncoveredLineNumbers, table).length), 0);
+      MathMax(acc, formatUncoveredLines(getUncoveredLines(file.lines), table).length), 0);
     uncoveredLinesPadLength = MathMax(uncoveredLinesPadLength, 'uncovered lines'.length);
     const uncoveredLinesWidth = uncoveredLinesPadLength + 2;
 
@@ -394,7 +399,7 @@ function getCoverageReport(pad, summary, symbol, color, table) {
 
     report += `${prefix}${getCell(relativePath, filePadLength, StringPrototypePadEnd, truncateStart, fileCoverage)}${kSeparator}` +
               `${ArrayPrototypeJoin(ArrayPrototypeMap(coverages, (coverage, j) => getCell(NumberPrototypeToFixed(coverage, 2), columnPadLengths[j], StringPrototypePadStart, false, coverage)), kSeparator)}${kSeparator}` +
-              `${getCell(formatUncoveredLines(file.uncoveredLineNumbers, table), uncoveredLinesPadLength, false, truncateEnd)}\n`;
+              `${getCell(formatUncoveredLines(getUncoveredLines(file.lines), table), uncoveredLinesPadLength, false, truncateEnd)}\n`;
   }
 
   // Foot

test/fixtures/test-runner/custom_reporters/coverage.mjs

@@ -0,0 +1,15 @@
+import { Transform } from 'node:stream';
+
+export default class CoverageReporter extends Transform {
+  constructor(options) {
+    super({ ...options, writableObjectMode: true });
+  }
+
+  _transform(event, _encoding, callback) {
+    if (event.type === 'test:coverage') {
+      callback(null, JSON.stringify(event.data, null, 2));
+    } else {
+      callback(null);
+    }
+  }
+}

test/parallel/test-runner-coverage.js

@@ -181,3 +181,59 @@ test('coverage is combined for multiple processes', skipIfNoInspector, () => {
   assert(result.stdout.toString().includes(report));
   assert.strictEqual(result.status, 0);
 });
+
+test('coverage reports on lines, functions, and branches', skipIfNoInspector, async (t) => {
+  const fixture = fixtures.path('test-runner', 'coverage.js');
+  const child = spawnSync(process.execPath,
+                          ['--test', '--experimental-test-coverage', '--test-reporter',
+                           fixtures.fileURL('test-runner/custom_reporters/coverage.mjs'),
+                           fixture]);
+  assert.strictEqual(child.stderr.toString(), '');
+  const stdout = child.stdout.toString();
+  const coverage = JSON.parse(stdout);
+
+  await t.test('does not include node_modules', () => {
+    assert.strictEqual(coverage.summary.files.length, 3);
+    const files = ['coverage.js', 'invalid-tap.js', 'throw.js'];
+    coverage.summary.files.forEach((file, index) => {
+      assert.ok(file.path.endsWith(files[index]));
+    });
+  });
+
+  const file = coverage.summary.files[0];
+
+  await t.test('reports on function coverage', () => {
+    const uncalledFunction = file.functions.find((f) => f.name === 'uncalledTopLevelFunction');
+    assert.strictEqual(uncalledFunction.count, 0);
+    assert.strictEqual(uncalledFunction.line, 16);
+
+    const calledTwice = file.functions.find((f) => f.name === 'fnWithControlFlow');
+    assert.strictEqual(calledTwice.count, 2);
+    assert.strictEqual(calledTwice.line, 35);
+  });
+
+  await t.test('reports on branch coverage', () => {
+    const uncalledBranch = file.branches.find((b) => b.line === 6);
+    assert.strictEqual(uncalledBranch.count, 0);
+
+    const calledTwice = file.branches.find((b) => b.line === 35);
+    assert.strictEqual(calledTwice.count, 2);
+  });
+
+  await t.test('reports on line coverage', () => {
+    [
+      { line: 36, count: 2 },
+      { line: 37, count: 1 },
+      { line: 38, count: 1 },
+      { line: 39, count: 0 },
+      { line: 40, count: 1 },
+      { line: 41, count: 1 },
+      { line: 42, count: 1 },
+      { line: 43, count: 0 },
+      { line: 44, count: 0 },
+    ].forEach((line) => {
+      const testLine = file.lines.find((l) => l.line === line.line);
+      assert.strictEqual(testLine.count, line.count);
+    });
+  });
+});