feat(jest-core): Add newline after Json output (#13817)

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Features
 
+- `[jest-core]` Add newlines to JSON output ([#13817](https://github.com/facebook/jest/pull/13817))
+
 ### Fixes
 
 - `[@jest/expect-utils]` `toMatchObject` diffs should include `Symbol` properties ([#13810](https://github.com/facebook/jest/pull/13810))

e2e/__tests__/jsonReporter.test.ts

@@ -28,6 +28,8 @@ describe('JSON Reporter', () => {
     runJest('json-reporter', ['--json', `--outputFile=${outputFileName}`]);
     const testOutput = fs.readFileSync(outputFilePath, 'utf8');
 
+    expect(testOutput.endsWith('\n')).toBe(true);
+
     try {
       jsonResult = JSON.parse(testOutput);
     } catch (err: any) {
@@ -71,12 +73,16 @@ describe('JSON Reporter', () => {
   });
 
   it('outputs coverage report', () => {
-    const result = runJest('json-reporter', ['--json']);
+    const result = runJest('json-reporter', ['--json'], {
+      keepTrailingNewline: true,
+    });
     let jsonResult: FormattedTestResults;
 
     expect(result.stderr).toMatch(/1 failed, 1 skipped, 2 passed/);
     expect(result.exitCode).toBe(1);
 
+    expect(result.stdout.endsWith('\n')).toBe(true);
+
     try {
       jsonResult = JSON.parse(result.stdout);
     } catch (err: any) {

e2e/runJest.ts

@@ -20,6 +20,7 @@ import {normalizeIcons} from './Utils';
 const JEST_PATH = path.resolve(__dirname, '../packages/jest-cli/bin/jest.js');
 
 type RunJestOptions = {
+  keepTrailingNewline?: boolean; // keep final newline in output from stdout and stderr
   nodeOptions?: string;
   nodePath?: string;
   skipPkgJsonCheck?: boolean; // don't complain if can't find package.json
@@ -97,6 +98,7 @@ function spawnJest(
     cwd: dir,
     env,
     reject: false,
+    stripFinalNewline: !options.keepTrailingNewline,
     timeout: options.timeout || 0,
   };
 

packages/jest-core/src/runJest.ts

@@ -106,12 +106,17 @@ const processResults = async (
       const cwd = tryRealpath(process.cwd());
       const filePath = path.resolve(cwd, outputFile);
 
-      fs.writeFileSync(filePath, JSON.stringify(formatTestResults(runResults)));
+      fs.writeFileSync(
+        filePath,
+        `${JSON.stringify(formatTestResults(runResults))}\n`,
+      );
       outputStream.write(
         `Test results written to: ${path.relative(cwd, filePath)}\n`,
       );
     } else {
-      process.stdout.write(JSON.stringify(formatTestResults(runResults)));
+      process.stdout.write(
+        `${JSON.stringify(formatTestResults(runResults))}\n`,
+      );
     }
   }