add std out to subprocess to stop overflow (#21758)

Displays output to the user and ensures the subprocess doesn't run into
buffer overflow. Bug was introduced with the switch to the
execObservable in #21667.
Only occurs for large repos where output from pytest was large enough to
reach buffer overflow.

pythonFiles/tests/pytestadapter/test_execution.py

@@ -1,6 +1,5 @@
 # Copyright (c) Microsoft Corporation. All rights reserved.
 # Licensed under the MIT License.
-import json
 import os
 import shutil
 

src/client/testing/testController/common/server.ts

@@ -209,7 +209,16 @@ export class PythonTestServer implements ITestServer, Disposable {
                 runInstance?.token.onCancellationRequested(() => {
                     result?.proc?.kill();
                 });
-                result?.proc?.on('close', () => {
+
+                // Take all output from the subprocess and add it to the test output channel. This will be the pytest output.
+                // Displays output to user and ensure the subprocess doesn't run into buffer overflow.
+                result?.proc?.stdout?.on('data', (data) => {
+                    spawnOptions?.outputChannel?.append(data);
+                });
+                result?.proc?.stderr?.on('data', (data) => {
+                    spawnOptions?.outputChannel?.append(data);
+                });
+                result?.proc?.on('exit', () => {
                     traceLog('Exec server closed.', uuid);
                     deferred.resolve({ stdout: '', stderr: '' });
                     callback?.();

src/client/testing/testController/pytest/pytestDiscoveryAdapter.ts

@@ -86,7 +86,15 @@ export class PytestTestDiscoveryAdapter implements ITestDiscoveryAdapter {
         const execArgs = ['-m', 'pytest', '-p', 'vscode_pytest', '--collect-only'].concat(pytestArgs);
         const result = execService?.execObservable(execArgs, spawnOptions);
 
-        result?.proc?.on('close', () => {
+        // Take all output from the subprocess and add it to the test output channel. This will be the pytest output.
+        // Displays output to user and ensure the subprocess doesn't run into buffer overflow.
+        result?.proc?.stdout?.on('data', (data) => {
+            spawnOptions.outputChannel?.append(data);
+        });
+        result?.proc?.stderr?.on('data', (data) => {
+            spawnOptions.outputChannel?.append(data);
+        });
+        result?.proc?.on('exit', () => {
             deferredExec.resolve({ stdout: '', stderr: '' });
             deferred.resolve();
         });

src/client/testing/testController/pytest/pytestExecutionAdapter.ts

@@ -166,6 +166,15 @@ export class PytestTestExecutionAdapter implements ITestExecutionAdapter {
                     result?.proc?.kill();
                 });
 
+                // Take all output from the subprocess and add it to the test output channel. This will be the pytest output.
+                // Displays output to user and ensure the subprocess doesn't run into buffer overflow.
+                result?.proc?.stdout?.on('data', (data) => {
+                    this.outputChannel?.append(data);
+                });
+                result?.proc?.stderr?.on('data', (data) => {
+                    this.outputChannel?.append(data);
+                });
+
                 result?.proc?.on('close', () => {
                     deferredExec.resolve({ stdout: '', stderr: '' });
                     deferred.resolve();

src/test/mocks/helper.ts

@@ -0,0 +1,11 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+import { Readable } from 'stream';
+
+export class FakeReadableStream extends Readable {
+    _read(_size: unknown): void | null {
+        // custom reading logic here
+        this.push(null); // end the stream
+    }
+}

src/test/mocks/mockChildProcess.ts

@@ -1,17 +1,18 @@
 /* eslint-disable @typescript-eslint/no-unused-vars */
 /* eslint-disable @typescript-eslint/no-explicit-any */
 import { Serializable, SendHandle, MessageOptions } from 'child_process';
-import { Writable, Readable, Pipe } from 'stream';
 import { EventEmitter } from 'node:events';
+import { Writable, Readable, Pipe } from 'stream';
+import { FakeReadableStream } from './helper';
 
 export class MockChildProcess extends EventEmitter {
     constructor(spawnfile: string, spawnargs: string[]) {
         super();
         this.spawnfile = spawnfile;
         this.spawnargs = spawnargs;
         this.stdin = new Writable();
-        this.stdout = new Readable();
-        this.stderr = null;
+        this.stdout = new FakeReadableStream();
+        this.stderr = new FakeReadableStream();
         this.channel = null;
         this.stdio = [this.stdin, this.stdout, this.stdout, this.stderr, null];
         this.killed = false;