fix(reporters): enforce 80 column limit fallback for coverage table i…

CHANGELOG.md

@@ -13,6 +13,7 @@
 - `[@jest-environment/jsdom-abstract]` Make `@types/jsdom` a peer dependency ([#16166](https://github.com/jestjs/jest/pull/16166))
 - `[jest-runtime]` Fall back to native ESM when a `.js` file contains ESM syntax but has no `"type":"module"` marker ([#16152](https://github.com/jestjs/jest/pull/16152))
 - `[jest-runtime]` Support older test environments whose `moduleMocker` does not implement `clearMocksOnScope` ([#16169](https://github.com/jestjs/jest/pull/16169))
+- `[jest-reporters]` Fix coverage report table formatting in CI/GitHub Actions environments where `process.stdout.columns` is undefined by falling back to the `COLUMNS` env var or `80` columns in CI, preserving existing behaviour in other non-TTY environments ([#16227](https://github.com/jestjs/jest/pull/16227))
 
 ### Chore & Maintenance
 

packages/jest-reporters/src/CoverageReporter.ts

@@ -87,7 +87,14 @@ export default class CoverageReporter extends BaseReporter {
         }
         istanbulReports
           .create(reporter, {
-            maxCols: process.stdout.columns || Number.POSITIVE_INFINITY,
+            maxCols:
+              process.stdout.columns ||
+              Number.parseInt(process.env.COLUMNS || '', 10) ||
+              ((process.env.CI === 'true' ||
+                process.env.GITHUB_ACTIONS === 'true') &&
+              !process.env.JEST_WORKER_ID
+                ? 80
+                : Number.POSITIVE_INFINITY),
             ...additionalOptions,
           })
           .execute(reportContext);

packages/jest-reporters/src/__tests__/CoverageReporter.test.js

@@ -454,12 +454,64 @@ describe('onRunComplete', () => {
     await testReporter.onRunComplete(new Set(), {}, mockAggResults);
 
     expect(istanbulReports.create).toHaveBeenCalledWith('json', {
-      maxCols: process.stdout.columns || Number.POSITIVE_INFINITY,
+      maxCols:
+        process.stdout.columns ||
+        Number.parseInt(process.env.COLUMNS || '', 10) ||
+        ((process.env.CI === 'true' || process.env.GITHUB_ACTIONS === 'true') &&
+        !process.env.JEST_WORKER_ID
+          ? 80
+          : Number.POSITIVE_INFINITY),
     });
     expect(istanbulReports.create).toHaveBeenCalledWith('lcov', {
       maxCols: 10,
       projectRoot: './',
     });
     expect(testReporter.getLastError()).toBeUndefined();
   });
+
+  describe('maxCols fallback logic in CI', () => {
+    const originalEnv = process.env;
+
+    beforeEach(() => {
+      jest.resetModules();
+      process.env = {...originalEnv};
+      delete process.env.COLUMNS;
+    });
+
+    afterEach(() => {
+      process.env = originalEnv;
+    });
+
+    test('falls back to 80 in CI without JEST_WORKER_ID', async () => {
+      process.env.CI = 'true';
+      delete process.env.JEST_WORKER_ID;
+
+      const testReporter = new CoverageReporter({
+        coverageReporters: ['json'],
+      });
+      testReporter.log = jest.fn();
+
+      await testReporter.onRunComplete(new Set(), {}, mockAggResults);
+
+      expect(istanbulReports.create).toHaveBeenCalledWith('json', {
+        maxCols: process.stdout.columns || 80,
+      });
+    });
+
+    test('falls back to Infinity in CI with JEST_WORKER_ID', async () => {
+      process.env.CI = 'true';
+      process.env.JEST_WORKER_ID = '1';
+
+      const testReporter = new CoverageReporter({
+        coverageReporters: ['json'],
+      });
+      testReporter.log = jest.fn();
+
+      await testReporter.onRunComplete(new Set(), {}, mockAggResults);
+
+      expect(istanbulReports.create).toHaveBeenCalledWith('json', {
+        maxCols: process.stdout.columns || Number.POSITIVE_INFINITY,
+      });
+    });
+  });
 });