CustomConsole: print console.error and console.assert to stderr (#8261)

* CustomConsole: print console.error and console.assert to stderr
* Print to stderr when using console.warn
* Fix difference between node versions

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ### Fixes
 
+- `[@jest/console]` Print to stderr when calling `console.error`, `console.warn` or `console.assert` using the `jest-runtime` CLI ([#8261](https://github.com/facebook/jest/pull/8261))
+
 ### Chore & Maintenance
 
 ### Performance

packages/jest-console/src/CustomConsole.ts

@@ -12,8 +12,8 @@ import chalk from 'chalk';
 import {LogCounters, LogMessage, LogTimers, LogType} from './types';
 
 // TODO: Copied from `jest-util`. Import from it in Jest 25
-function clearLine(stream: NodeJS.WritableStream) {
-  if (process.stdout.isTTY) {
+function clearLine(stream: NodeJS.WritableStream & {isTTY?: boolean}) {
+  if (stream.isTTY) {
     stream.write('\x1b[999D\x1b[K');
   }
 }
@@ -22,6 +22,7 @@ type Formatter = (type: LogType, message: LogMessage) => string;
 
 export default class CustomConsole extends Console {
   private _stdout: NodeJS.WritableStream;
+  private _stderr: NodeJS.WritableStream;
   private _formatBuffer: Formatter;
   private _counters: LogCounters;
   private _timers: LogTimers;
@@ -34,19 +35,23 @@ export default class CustomConsole extends Console {
   ) {
     super(stdout, stderr);
     this._stdout = stdout;
+    this._stderr = stderr;
     this._formatBuffer = formatBuffer;
     this._counters = {};
     this._timers = {};
     this._groupDepth = 0;
   }
 
-  private _logToParentConsole(message: string) {
-    super.log(message);
-  }
-
   private _log(type: LogType, message: string) {
     clearLine(this._stdout);
-    this._logToParentConsole(
+    super.log(
+      this._formatBuffer(type, '  '.repeat(this._groupDepth) + message),
+    );
+  }
+
+  private _logError(type: LogType, message: string) {
+    clearLine(this._stderr);
+    super.error(
       this._formatBuffer(type, '  '.repeat(this._groupDepth) + message),
     );
   }
@@ -55,7 +60,7 @@ export default class CustomConsole extends Console {
     try {
       assert(value, message);
     } catch (error) {
-      this._log('assert', error.toString());
+      this._logError('assert', error.toString());
     }
   }
 
@@ -84,7 +89,7 @@ export default class CustomConsole extends Console {
   }
 
   error(firstArg: any, ...args: Array<any>) {
-    this._log('error', format(firstArg, ...args));
+    this._logError('error', format(firstArg, ...args));
   }
 
   group(title?: string, ...args: Array<any>) {
@@ -137,7 +142,7 @@ export default class CustomConsole extends Console {
   }
 
   warn(firstArg: any, ...args: Array<any>) {
-    this._log('warn', format(firstArg, ...args));
+    this._logError('warn', format(firstArg, ...args));
   }
 
   getBuffer() {

packages/jest-console/src/__tests__/console.test.ts → packages/jest-console/src/__tests__/CustomConsole.test.ts

@@ -5,47 +5,88 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import {Writable} from 'stream';
 import chalk from 'chalk';
 import CustomConsole from '../CustomConsole';
 
 describe('CustomConsole', () => {
   let _console;
-  let _stdout = '';
+  let _stdout;
+  let _stderr;
 
   beforeEach(() => {
-    _console = new CustomConsole(process.stdout, process.stderr);
-    jest.spyOn(_console, '_logToParentConsole').mockImplementation(message => {
-      _stdout += message + '\n';
+    _stdout = '';
+    _stderr = '';
+
+    const stdout = new Writable({
+      write(chunk, encoding, callback) {
+        _stdout += chunk.toString();
+        callback();
+      },
     });
 
-    _stdout = '';
+    const stderr = new Writable({
+      write(chunk, encoding, callback) {
+        _stderr += chunk.toString();
+        callback();
+      },
+    });
+
+    _console = new CustomConsole(stdout, stderr);
+  });
+
+  describe('log', () => {
+    test('should print to stdout', () => {
+      _console.log('Hello world!');
+
+      expect(_stdout).toBe('Hello world!\n');
+    });
+  });
+
+  describe('error', () => {
+    test('should print to stderr', () => {
+      _console.error('Found some error!');
+
+      expect(_stderr).toBe('Found some error!\n');
+    });
+  });
+
+  describe('warn', () => {
+    test('should print to stderr', () => {
+      _console.warn('Found some warning!');
+
+      expect(_stderr).toBe('Found some warning!\n');
+    });
   });
 
   describe('assert', () => {
     test('do not log when the assertion is truthy', () => {
       _console.assert(true);
 
-      expect(_stdout).toMatch('');
+      expect(_stderr).toMatch('');
     });
 
     test('do not log when the assertion is truthy and there is a message', () => {
       _console.assert(true, 'ok');
 
-      expect(_stdout).toMatch('');
+      expect(_stderr).toMatch('');
     });
 
     test('log the assertion error when the assertion is falsy', () => {
       _console.assert(false);
 
-      expect(_stdout).toMatch('AssertionError');
-      expect(_stdout).toMatch('false == true');
+      expect(_stderr).toMatch('AssertionError');
+      expect(_stderr).toMatch(
+        // The message may differ across Node versions
+        /(false == true)|(The expression evaluated to a falsy value:)/,
+      );
     });
 
     test('log the assertion error when the assertion is falsy with another message argument', () => {
-      _console.assert(false, 'ok');
+      _console.assert(false, 'this should not happen');
 
-      expect(_stdout).toMatch('AssertionError');
-      expect(_stdout).toMatch('ok');
+      expect(_stderr).toMatch('AssertionError');
+      expect(_stderr).toMatch('this should not happen');
     });
   });
 

packages/jest-runner/src/runTest.ts

@@ -135,13 +135,9 @@ async function runTestInternal(
   let testConsole;
 
   if (globalConfig.silent) {
-    testConsole = new NullConsole(consoleOut, process.stderr, consoleFormatter);
+    testConsole = new NullConsole(consoleOut, consoleOut, consoleFormatter);
   } else if (globalConfig.verbose) {
-    testConsole = new CustomConsole(
-      consoleOut,
-      process.stderr,
-      consoleFormatter,
-    );
+    testConsole = new CustomConsole(consoleOut, consoleOut, consoleFormatter);
   } else {
     testConsole = new BufferedConsole(() => runtime && runtime.getSourceMaps());
   }