test_runner: merge call counts of functions without block coverage

lib/internal/test_runner/coverage.js

@@ -754,19 +754,17 @@ function mergeCoverageScripts(oldScript, newScript) {
         // These are the same functions.
         found = true;
 
-        // If newFn is block level coverage, then it will:
-        // - Replace oldFn if oldFn is not block level coverage.
-        // - Merge with oldFn if it is also block level coverage.
-        // If newFn is not block level coverage, then it has no new data.
-        if (newFn.isBlockCoverage) {
-          if (oldFn.isBlockCoverage) {
-            // Merge the oldFn ranges with the newFn ranges.
-            mergeCoverageRanges(oldFn, newFn);
-          } else {
-            // Replace oldFn with newFn.
+        if (newFn.isBlockCoverage && oldFn.isBlockCoverage) {
+          mergeCoverageRanges(oldFn, newFn);
+        } else {
+          // A function without block level coverage only has a call count.
+          // Keep the block level ranges if either side has them.
+          const count = oldFn.ranges[0].count + newFn.ranges[0].count;
+          if (newFn.isBlockCoverage) {
             oldFn.isBlockCoverage = true;
             oldFn.ranges = newFn.ranges;
           }
+          oldFn.ranges[0].count = count;
         }
 
         break;

test/fixtures/test-runner/coverage-function-counts/lib.js

@@ -0,0 +1,4 @@
+function a() {}
+function b() {}
+function c() {}
+function d() {}

test/fixtures/test-runner/coverage-function-counts/test.js

@@ -0,0 +1,25 @@
+'use strict';
+const { writeFileSync } = require('node:fs');
+const { join } = require('node:path');
+const { pathToFileURL } = require('node:url');
+
+function fn(functionName, startOffset, count, isBlockCoverage = false) {
+  const endOffset = functionName ? startOffset + 15 : 64;
+  return { functionName, ranges: [{ startOffset, endOffset, count }], isBlockCoverage };
+}
+
+function writeCoverage(id, functions) {
+  writeFileSync(
+    join(process.env.NODE_V8_COVERAGE, `coverage-${id}-0000000000000-0.json`),
+    JSON.stringify({
+      result: [{
+        scriptId: '1',
+        url: pathToFileURL(join(__dirname, 'lib.js')).href,
+        functions: [fn('', 0, 1), ...functions],
+      }],
+    }),
+  );
+}
+
+writeCoverage(1, [fn('a', 0, 1), fn('b', 16, 0), fn('c', 32, 1), fn('d', 48, 0, true)]);
+writeCoverage(2, [fn('a', 0, 0), fn('b', 16, 1), fn('c', 32, 0, true), fn('d', 48, 1)]);

test/parallel/test-runner-coverage.js

@@ -657,3 +657,21 @@ test('coverage with directory and file named "file"', skipIfNoInspector, () => {
   assert.strictEqual(result.status, 0);
   assertIncludesReport(result, 'start of coverage report');
 });
+
+test('merges call counts of functions without block coverage', skipIfNoInspector, () => {
+  const args = [
+    '--test',
+    '--experimental-test-coverage',
+    '--test-coverage-exclude=!test/**',
+    '--test-reporter',
+    'tap',
+    'test.js',
+  ];
+  const result = spawnSync(process.execPath, args, {
+    cwd: fixtures.path('test-runner', 'coverage-function-counts'),
+  });
+
+  assert.strictEqual(result.stderr.toString(), '');
+  assert.strictEqual(result.status, 0);
+  assert.match(result.stdout.toString(), /# lib\.js +\| 100\.00 \| +100\.00 \| +100\.00 \|/);
+});