Support JSON line output.

docs/CLI.md

@@ -190,7 +190,13 @@ Generate a basic configuration file. Based on your project, Jest will ask you a
 
 ### `--json`
 
-Prints the test results in JSON. This mode will send all other test output and user messages to stderr.
+Prints the test results as JSON. This mode will send all other console output to stderr.
+
+### `--jsonLines`
+
+Prints the test results as JSON lines. This mode will send all other console output to stderr.
+
+This format is ideal for handling very large test suites, where creating or consuming a single very large JSON object with all results and coverage data may cause memory issues.
 
 ### `--outputFile=<filename>`
 

e2e/__tests__/__snapshots__/showConfig.test.ts.snap

@@ -102,6 +102,7 @@ exports[`--showConfig outputs config info and exits 1`] = `
     "globalSetup": null,
     "globalTeardown": null,
     "json": false,
+    "jsonLines": false,
     "listTests": false,
     "maxConcurrency": 5,
     "maxWorkers": "[maxWorkers]",

packages/jest-cli/src/cli/args.ts

@@ -301,8 +301,15 @@ export const options = {
   json: {
     default: undefined,
     description:
-      'Prints the test results in JSON. This mode will send all ' +
-      'other test output and user messages to stderr.',
+      'Prints the test results as JSON. This mode will send all other ' +
+      'console output to stderr.',
+    type: 'boolean' as 'boolean',
+  },
+  jsonLines: {
+    default: undefined,
+    description:
+      'Prints the test results as JSON lines. This mode will send all other ' +
+      'console output to stderr.',
     type: 'boolean' as 'boolean',
   },
   lastCommit: {

packages/jest-config/src/index.ts

@@ -123,6 +123,7 @@ const groupOptions = (
     globalSetup: options.globalSetup,
     globalTeardown: options.globalTeardown,
     json: options.json,
+    jsonLines: options.jsonLines,
     lastCommit: options.lastCommit,
     listTests: options.listTests,
     logHeapUsage: options.logHeapUsage,

packages/jest-config/src/normalize.ts

@@ -874,6 +874,7 @@ export default function normalize(
   newOptions.nonFlagArgs = argv._;
   newOptions.testPathPattern = buildTestPathPattern(argv);
   newOptions.json = !!argv.json;
+  newOptions.jsonLines = !!argv.jsonLines;
 
   newOptions.testFailureExitCode = parseInt(
     (newOptions.testFailureExitCode as unknown) as string,

packages/jest-core/src/lib/log_debug_messages.ts

@@ -19,5 +19,9 @@ export default function logDebugMessages(
     globalConfig,
     version: VERSION,
   };
-  outputStream.write(JSON.stringify(output, null, '  ') + '\n');
+
+  // Write to single line if using JSON lines format. Otherwise, pretty print.
+  outputStream.write(
+    JSON.stringify(output, null, !globalConfig.jsonLines ? '  ' : '') + '\n',
+  );
 }

packages/jest-core/src/runJest.ts

@@ -9,7 +9,6 @@ import path from 'path';
 import chalk from 'chalk';
 import {sync as realpath} from 'realpath-native';
 import {CustomConsole} from '@jest/console';
-import {formatTestResults} from 'jest-util';
 import exit from 'exit';
 import fs from 'graceful-fs';
 import {JestHook, JestHookEmitter} from 'jest-watcher';
@@ -19,6 +18,8 @@ import {Config} from '@jest/types';
 import {
   AggregatedResult,
   makeEmptyAggregatedTestResult,
+  formatTestResult,
+  formatTestResults,
 } from '@jest/test-result';
 import {ChangedFiles, ChangedFilesPromise} from 'jest-changed-files';
 import getNoTestsFoundMessage from './getNoTestsFoundMessage';
@@ -69,20 +70,40 @@ const getTestPaths = async (
 
 type ProcessResultOptions = Pick<
   Config.GlobalConfig,
-  'json' | 'outputFile' | 'testResultsProcessor'
+  'json' | 'jsonLines' | 'outputFile' | 'testResultsProcessor'
 > & {
   collectHandles?: () => Array<Error>;
   onComplete?: (result: AggregatedResult) => void;
   outputStream: NodeJS.WritableStream;
 };
 
-const processResults = (
+const stdoutWriteBuffered = (data: string) =>
+  new Promise<void>(resolve => {
+    if (!process.stdout.write(data)) {
+      process.stdout.once('drain', resolve);
+    } else {
+      process.nextTick(resolve);
+    }
+  });
+
+const getOutputFilePaths = (outputFile: string) => {
+  const cwd = realpath(process.cwd());
+  const absoluteOutputFile = path.resolve(cwd, outputFile);
+  const relativeOutputFile = path.relative(cwd, absoluteOutputFile);
+  return {
+    absoluteOutputFile,
+    relativeOutputFile,
+  };
+};
+
+const processResults = async (
   runResults: AggregatedResult,
   options: ProcessResultOptions,
 ) => {
   const {
     outputFile,
     json: isJSON,
+    jsonLines: isJSONLines,
     onComplete,
     outputStream,
     testResultsProcessor,
@@ -98,14 +119,73 @@ const processResults = (
   if (testResultsProcessor) {
     runResults = require(testResultsProcessor)(runResults);
   }
-  if (isJSON) {
+  if (isJSONLines) {
+    let writeLine: (line: string) => Promise<void>;
+    let onWriteFinished: (() => void) | undefined = undefined;
     if (outputFile) {
-      const cwd = realpath(process.cwd());
-      const filePath = path.resolve(cwd, outputFile);
+      const {absoluteOutputFile, relativeOutputFile} = getOutputFilePaths(
+        outputFile,
+      );
+      fs.writeFileSync(absoluteOutputFile, '');
+      writeLine = line =>
+        new Promise<void>((resolve, reject) =>
+          fs.appendFile(absoluteOutputFile, line + '\n', {}, err => {
+            if (err) {
+              reject(err);
+              return;
+            }
+            resolve();
+          }),
+        );
+      onWriteFinished = () => {
+        outputStream.write(
+          `Test results written as JSON lines to: ${relativeOutputFile}\n`,
+        );
+      };
+    } else {
+      writeLine = line => stdoutWriteBuffered(line + '\n');
+    }
 
-      fs.writeFileSync(filePath, JSON.stringify(formatTestResults(runResults)));
+    await writeLine(
+      JSON.stringify({
+        runResults: {
+          ...runResults,
+          coverageMap: undefined,
+          testResults: undefined,
+        },
+      }),
+    );
+    for (const testResult of runResults.testResults) {
+      await writeLine(
+        JSON.stringify({testResults: formatTestResult(testResult)}),
+      );
+    }
+    if (runResults.coverageMap) {
+      const coverageMap: {[key: string]: unknown} =
+        typeof runResults.coverageMap.toJSON === 'function'
+          ? runResults.coverageMap.toJSON()
+          : runResults.coverageMap;
+      const coverageMapFiles = Object.keys(coverageMap);
+      for (const coverageMapFile of coverageMapFiles) {
+        await writeLine(
+          JSON.stringify({coverageMap: coverageMap[coverageMapFile]}),
+        );
+      }
+    }
+    if (onWriteFinished) {
+      onWriteFinished();
+    }
+  } else if (isJSON) {
+    if (outputFile) {
+      const {absoluteOutputFile, relativeOutputFile} = getOutputFilePaths(
+        outputFile,
+      );
+      fs.writeFileSync(
+        absoluteOutputFile,
+        JSON.stringify(formatTestResults(runResults)),
+      );
       outputStream.write(
-        `Test results written to: ${path.relative(cwd, filePath)}\n`,
+        `Test results written as JSON to: ${relativeOutputFile}\n`,
       );
     } else {
       process.stdout.write(JSON.stringify(formatTestResults(runResults)));
@@ -183,7 +263,11 @@ export default (async function runJest({
 
   if (globalConfig.listTests) {
     const testsPaths = Array.from(new Set(allTests.map(test => test.path)));
-    if (globalConfig.json) {
+    if (globalConfig.jsonLines) {
+      for (const testPath of testsPaths) {
+        console.log(JSON.stringify({testPath}));
+      }
+    } else if (globalConfig.json) {
       console.log(JSON.stringify(testsPaths));
     } else {
       console.log(testsPaths.join('\n'));
@@ -253,9 +337,10 @@ export default (async function runJest({
     await runGlobalHook({allTests, globalConfig, moduleName: 'globalTeardown'});
   }
 
-  return processResults(results, {
+  return await processResults(results, {
     collectHandles,
     json: globalConfig.json,
+    jsonLines: globalConfig.jsonLines,
     onComplete,
     outputFile: globalConfig.outputFile,
     outputStream,

packages/jest-phabricator/src/index.ts

@@ -5,15 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {AggregatedResult} from '@jest/test-result';
-
-type CoverageMap = AggregatedResult['coverageMap'];
-
-function summarize(coverageMap: CoverageMap): CoverageMap {
-  if (!coverageMap) {
-    return coverageMap;
-  }
+import {AggregatedResult, CoverageMap} from '@jest/test-result';
 
+function summarize(
+  coverageMap: CoverageMap,
+): {[key: string]: {[key: string]: unknown}} {
   const summaries = Object.create(null);
 
   coverageMap.files().forEach(file => {
@@ -32,12 +28,20 @@ function summarize(coverageMap: CoverageMap): CoverageMap {
       }
     }
 
-    summaries[file] = covered.join('');
+    summaries[file] = {
+      path: file,
+    };
   });
 
   return summaries;
 }
 
 export = function(results: AggregatedResult): AggregatedResult {
-  return {...results, coverageMap: summarize(results.coverageMap)};
+  return {
+    ...results,
+    coverageMap:
+      results.coverageMap && typeof results.coverageMap.toJSON === 'function'
+        ? summarize(results.coverageMap as CoverageMap)
+        : results.coverageMap,
+  };
 };

packages/jest-test-result/src/formatTestResults.ts

@@ -16,7 +16,7 @@ import {
   TestResult,
 } from './types';
 
-const formatTestResult = (
+export const formatTestResult = (
   testResult: TestResult,
   codeCoverageFormatter?: CodeCoverageFormatter,
   reporter?: CodeCoverageReporter,

packages/jest-test-result/src/index.ts

@@ -5,7 +5,10 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-export {default as formatTestResults} from './formatTestResults';
+export {
+  default as formatTestResults,
+  formatTestResult,
+} from './formatTestResults';
 export {
   addResult,
   buildFailureTestResult,
@@ -23,3 +26,4 @@ export {
   Suite,
   TestResult,
 } from './types';
+export {CoverageMap} from 'istanbul-lib-coverage';

packages/jest-test-result/src/types.ts

@@ -91,7 +91,7 @@ export type AggregatedResultWithoutCoverage = {
 };
 
 export type AggregatedResult = AggregatedResultWithoutCoverage & {
-  coverageMap?: CoverageMap | null;
+  coverageMap?: CoverageMap | {[key: string]: {[key: string]: unknown}};
 };
 
 export type Suite = {
@@ -146,7 +146,10 @@ export type FormattedTestResult = {
 };
 
 export type FormattedTestResults = {
-  coverageMap?: CoverageMap | null | undefined;
+  coverageMap?:
+    | CoverageMap
+    | {[key: string]: {[key: string]: unknown}}
+    | undefined;
   numFailedTests: number;
   numFailedTestSuites: number;
   numPassedTests: number;

packages/jest-types/src/Config.ts

@@ -312,6 +312,7 @@ export type GlobalConfig = {
   findRelatedTests: boolean;
   forceExit: boolean;
   json: boolean;
+  jsonLines: boolean;
   globalSetup: string | null | undefined;
   globalTeardown: string | null | undefined;
   lastCommit: boolean;
@@ -446,6 +447,7 @@ export type Argv = Arguments<
     haste: string;
     init: boolean;
     json: boolean;
+    jsonLines: boolean;
     lastCommit: boolean;
     logHeapUsage: boolean;
     maxWorkers: number;

website/versioned_docs/version-22.x/CLI.md

@@ -164,7 +164,7 @@ Show the help information, similar to this page.
 
 ### `--json`
 
-Prints the test results in JSON. This mode will send all other test output and user messages to stderr.
+Prints the test results as JSON. This mode will send all other console output to stderr.
 
 ### `--outputFile=<filename>`
 

website/versioned_docs/version-23.x/CLI.md

@@ -176,7 +176,7 @@ Generate a basic configuration file. Based on your project, Jest will ask you a
 
 ### `--json`
 
-Prints the test results in JSON. This mode will send all other test output and user messages to stderr.
+Prints the test results as JSON. This mode will send all other console output to stderr.
 
 ### `--outputFile=<filename>`
 

website/versioned_docs/version-24.0/CLI.md

@@ -191,7 +191,7 @@ Generate a basic configuration file. Based on your project, Jest will ask you a
 
 ### `--json`
 
-Prints the test results in JSON. This mode will send all other test output and user messages to stderr.
+Prints the test results as JSON. This mode will send all other console output to stderr.
 
 ### `--outputFile=<filename>`
 

website/versioned_docs/version-24.1/CLI.md

@@ -191,7 +191,7 @@ Generate a basic configuration file. Based on your project, Jest will ask you a
 
 ### `--json`
 
-Prints the test results in JSON. This mode will send all other test output and user messages to stderr.
+Prints the test results as JSON. This mode will send all other console output to stderr.
 
 ### `--outputFile=<filename>`