test_runner: refactor coverage report output for readability

Add a "table" parameter to getCoverageReport.
Keep the tap coverage output intact.
Change the output by adding padding and truncating the tables' cells.
Add separation lines for table head/body/foot.
Group uncovered lines as ranges.
Add yellow color for coverage between 50 and 90.

Refs: nodejs#46674

Author: dmnsgn

lib/internal/test_runner/reporter/spec.js

@@ -120,7 +120,7 @@ class SpecReporter extends Transform {
       case 'test:diagnostic':
         return `${colors[type]}${this.#indent(data.nesting)}${symbols[type]}${data.message}${white}\n`;
       case 'test:coverage':
-        return getCoverageReport(this.#indent(data.nesting), data.summary, symbols['test:coverage'], blue);
+        return getCoverageReport(this.#indent(data.nesting), data.summary, symbols['test:coverage'], blue, true);
     }
   }
   _transform({ type, data }, encoding, callback) {

lib/internal/test_runner/utils.js

@@ -3,12 +3,18 @@ const {
   ArrayPrototypeJoin,
   ArrayPrototypeMap,
   ArrayPrototypePush,
+  ArrayPrototypeReduce,
   ObjectGetOwnPropertyDescriptor,
+  MathFloor,
+  MathMax,
+  MathMin,
   NumberPrototypeToFixed,
   SafePromiseAllReturnArrayLike,
   RegExp,
   RegExpPrototypeExec,
   SafeMap,
+  StringPrototypePadStart,
+  StringPrototypePadEnd,
 } = primordials;
 
 const { basename, relative } = require('path');
@@ -27,6 +33,13 @@ const {
 } = require('internal/errors');
 const { compose } = require('stream');
 
+const coverageColors = {
+  '__proto__': null,
+  'high': green,
+  'medium': '\u001b[33m',
+  'low': red,
+};
+
 const kMultipleCallbackInvocations = 'multipleCallbackInvocations';
 const kRegExpPattern = /^\/(.*)\/([a-z]*)$/;
 const kSupportedFileExtensions = /\.[cm]?js$/;
@@ -250,45 +263,130 @@ function countCompletedTest(test, harness = test.root.harness) {
 }
 
 
-function coverageThreshold(coverage, color) {
-  coverage = NumberPrototypeToFixed(coverage, 2);
-  if (color) {
-    if (coverage > 90) return `${green}${coverage}${color}`;
-    if (coverage < 50) return `${red}${coverage}${color}`;
-  }
-  return coverage;
+function addTableLine(prefix, width) {
+  return `${prefix}${'-'.repeat(width)}\n`;
+}
+
+function truncateStart(string, width) {
+  return string.length > width ? `\u2026${string.substring(string.length - width + 1, string.length)}` : string;
+}
+
+function truncateEnd(string, width) {
+  return string.length > width ? `${string.substring(0, width - 1)}\u2026` : string;
+}
+
+function formatLinesToRanges(values) {
+  return ArrayPrototypeMap(ArrayPrototypeReduce(values, (prev, current, index, array) => {
+    if ((index > 0) && ((current - array[index - 1]) === 1)) {
+      prev[prev.length - 1][1] = current;
+    } else {
+      prev.push([current]);
+    }
+    return prev;
+  }, []), (range) => range.join('-'));
+}
+
+function formatUncoveredLines(lines, table) {
+  if (table) return ArrayPrototypeJoin(formatLinesToRanges(lines), ' ');
+  return ArrayPrototypeJoin(lines, ', ');
 }
 
-function getCoverageReport(pad, summary, symbol, color) {
-  let report = `${color}${pad}${symbol}start of coverage report\n`;
+const kColumns = ['line %', 'branch %', 'funcs %'];
+const kColumnsKeys = ['coveredLinePercent', 'coveredBranchPercent', 'coveredFunctionPercent'];
+const kSeparator = ' | ';
+
+function getCoverageReport(pad, summary, symbol, color, table) {
+  const prefix = `${pad}${symbol}`;
+  let report = `${color}${prefix}start of coverage report\n`;
+
+  let filePadLength;
+  let columnPadLengths = [];
+  let uncoveredLinesPadLength;
+  let tableWidth;
+
+  if (table) {
+    // Get expected column sizes
+    filePadLength = table && ArrayPrototypeReduce(summary.files, (acc, file) =>
+      MathMax(acc, relative(summary.workingDirectory, file.path).length), 0);
+    filePadLength = MathMax(filePadLength, 'file'.length);
+    const fileWidth = filePadLength + 2;
+
+    columnPadLengths = ArrayPrototypeMap(kColumns, (column) => (table ? MathMax(column.length, 6) : 0));
+    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);
+    uncoveredLinesPadLength = MathMax(uncoveredLinesPadLength, 'uncovered lines'.length);
+    const uncoveredLinesWidth = uncoveredLinesPadLength + 2;
+
+    tableWidth = fileWidth + columnsWidth + uncoveredLinesWidth;
+
+    // Fit with sensible defaults
+    const availableWidth = (process.stdout.columns || 9000) - prefix.length;
+    const columnsExtras = tableWidth - availableWidth;
+    if (table && columnsExtras > 0) {
+      // Ensure file name is sufficiently visible
+      const minFilePad = MathMin(8, filePadLength);
+      filePadLength -= MathFloor(columnsExtras * 0.2);
+      filePadLength = MathMax(filePadLength, minFilePad);
+
+      // Get rest of available space, subtracting margins
+      uncoveredLinesPadLength = MathMax(availableWidth - columnsWidth - (filePadLength + 2) - 2, 1);
+
+      // Update table width
+      tableWidth = availableWidth;
+    } else {
+      uncoveredLinesPadLength = Infinity;
+    }
+  }
+
+
+  function getCell(string, width, { pad, truncate, coverage }) {
+    if (!table) return string;
+
+    let result = string;
+    if (pad) result = pad(result, width);
+    if (truncate) result = truncate(result, width);
+    if (color && coverage !== undefined) {
+      if (coverage > 90) return `${coverageColors.high}${result}${color}`;
+      if (coverage > 50) return `${coverageColors.medium}${result}${color}`;
+      return `${coverageColors.low}${result}${color}`;
+    }
+    return result;
+  }
 
-  report += `${pad}${symbol}file | line % | branch % | funcs % | uncovered lines\n`;
+  // Head
+  if (table) report += addTableLine(prefix, tableWidth);
+  report += `${prefix}${getCell('file', filePadLength, { pad: StringPrototypePadEnd, truncate: truncateEnd })}${kSeparator}` +
+            `${ArrayPrototypeJoin(ArrayPrototypeMap(kColumns, (column, i) => getCell(column, columnPadLengths[i], { pad: StringPrototypePadStart })), kSeparator)}${kSeparator}` +
+            `${getCell('uncovered lines', uncoveredLinesPadLength, { truncate: truncateEnd })}\n`;
+  if (table) report += addTableLine(prefix, tableWidth);
 
+  // Body
   for (let i = 0; i < summary.files.length; ++i) {
-    const {
-      path,
-      coveredLinePercent,
-      coveredBranchPercent,
-      coveredFunctionPercent,
-      uncoveredLineNumbers,
-    } = summary.files[i];
-    const relativePath = relative(summary.workingDirectory, path);
-    const lines = coverageThreshold(coveredLinePercent, color);
-    const branches = coverageThreshold(coveredBranchPercent, color);
-    const functions = coverageThreshold(coveredFunctionPercent, color);
-    const uncovered = ArrayPrototypeJoin(uncoveredLineNumbers, ', ');
-
-    report += `${pad}${symbol}${relativePath} | ${lines} | ${branches} | ` +
-              `${functions} | ${uncovered}\n`;
+    const file = summary.files[i];
+    const relativePath = relative(summary.workingDirectory, file.path);
+
+    let fileCoverage = 0;
+    const coverages = ArrayPrototypeMap(kColumnsKeys, (columnKey) => {
+      const percent = file[columnKey];
+      fileCoverage += percent;
+      return percent;
+    });
+    fileCoverage /= kColumnsKeys.length;
+
+    report += `${prefix}${getCell(relativePath, filePadLength, { pad: StringPrototypePadEnd, truncate: truncateStart, coverage: fileCoverage })}${kSeparator}` +
+              `${ArrayPrototypeJoin(ArrayPrototypeMap(coverages, (coverage, j) => getCell(NumberPrototypeToFixed(coverage, 2), columnPadLengths[j], { coverage, pad: StringPrototypePadStart })), kSeparator)}${kSeparator}` +
+              `${getCell(formatUncoveredLines(file.uncoveredLineNumbers, table), uncoveredLinesPadLength, { truncate: truncateEnd })}\n`;
   }
 
-  const { totals } = summary;
-  report += `${pad}${symbol}all files | ` +
-            `${coverageThreshold(totals.coveredLinePercent, color)} | ` +
-            `${coverageThreshold(totals.coveredBranchPercent, color)} | ` +
-            `${coverageThreshold(totals.coveredFunctionPercent, color)} |\n`;
+  // Foot
+  if (table) report += addTableLine(prefix, tableWidth);
+  report += `${prefix}${getCell('all files', filePadLength, { pad: StringPrototypePadEnd, truncate: truncateEnd })}${kSeparator}` +
+            `${ArrayPrototypeJoin(ArrayPrototypeMap(kColumnsKeys, (columnKey, j) => getCell(NumberPrototypeToFixed(summary.totals[columnKey], 2), columnPadLengths[j], { coverage: summary.totals[columnKey], pad: StringPrototypePadStart })), kSeparator)} |\n`;
+  if (table) report += addTableLine(prefix, tableWidth);
 
-  report += `${pad}${symbol}end of coverage report\n`;
+  report += `${prefix}end of coverage report\n`;
   if (color) {
     report += white;
   }

test/parallel/test-runner-coverage.js

@@ -41,16 +41,21 @@ function getTapCoverageFixtureReport() {
 }
 
 function getSpecCoverageFixtureReport() {
+  /* eslint-disable max-len */
   const report = [
     '\u2139 start of coverage report',
-    '\u2139 file | line % | branch % | funcs % | uncovered lines',
-    '\u2139 test/fixtures/test-runner/coverage.js | 78.65 | 38.46 | 60.00 | 12, ' +
-    '13, 16, 17, 18, 19, 20, 21, 22, 27, 39, 43, 44, 61, 62, 66, 67, 71, 72',
-    '\u2139 test/fixtures/test-runner/invalid-tap.js | 100.00 | 100.00 | 100.00 | ',
-    '\u2139 test/fixtures/v8-coverage/throw.js | 71.43 | 50.00 | 100.00 | 5, 6',
-    '\u2139 all files | 78.35 | 43.75 | 60.00 |',
+    '\u2139 -------------------------------------------------------------------------------------------------------------------',
+    '\u2139 file                                     | line % | branch % | funcs % | uncovered lines',
+    '\u2139 -------------------------------------------------------------------------------------------------------------------',
+    '\u2139 test/fixtures/test-runner/coverage.js    |  78.65 |    38.46 |   60.00 | 12-13 16-22 27 39 43-44 61-62 66-67 71-72',
+    '\u2139 test/fixtures/test-runner/invalid-tap.js | 100.00 |   100.00 |  100.00 | ',
+    '\u2139 test/fixtures/v8-coverage/throw.js       |  71.43 |    50.00 |  100.00 | 5-6',
+    '\u2139 -------------------------------------------------------------------------------------------------------------------',
+    '\u2139 all files                                |  78.35 |    43.75 |   60.00 |',
+    '\u2139 -------------------------------------------------------------------------------------------------------------------',
     '\u2139 end of coverage report',
   ].join('\n');
+  /* eslint-enable max-len */
 
   if (common.isWindows) {
     return report.replaceAll('/', '\\');