fix(workers): use advanced serialization by default in child process workers

Author: SimenB

CHANGELOG.md

@@ -32,6 +32,7 @@
 - `[jest-runtime]` [**BREAKING**] `Runtime.createHasteMap` now returns a promise ([#12008](https://github.com/facebook/jest/pull/12008))
 - `[@jest/schemas]` New module for JSON schemas for Jest's config ([#12384](https://github.com/facebook/jest/pull/12384))
 - `[jest-worker]` [**BREAKING**] Allow only absolute `workerPath` ([#12343](https://github.com/facebook/jest/pull/12343))
+- `[jest-worker]` [**BREAKING**] Default to advanced serialization when using child process workers ([#10983] (https://github.com/facebook/jest/pull/10983))
 - `[pretty-format]` New `maxWidth` parameter ([#12402](https://github.com/facebook/jest/pull/12402))
 
 ### Fixes

packages/jest-runner/src/index.ts

@@ -165,7 +165,8 @@ export default class TestRunner {
 
     const worker = new Worker(TEST_WORKER_PATH, {
       exposedMethods: ['worker'],
-      forkOptions: {stdio: 'pipe'},
+      // @ts-expect-error: option does not exist on the node 12 types
+      forkOptions: {serialization: 'json', stdio: 'pipe'},
       maxRetries: 3,
       numWorkers: this._globalConfig.maxWorkers,
       setupArgs: [

packages/jest-worker/README.md

@@ -73,7 +73,7 @@ List of method names that can be called on the child processes from the parent p
 
 #### `forkOptions: ForkOptions` (optional)
 
-Allow customizing all options passed to `child_process.fork`. By default, some values are set (`cwd`, `env` and `execArgv`), but you can override them and customize the rest. For a list of valid values, check [the Node documentation](https://nodejs.org/api/child_process.html#child_processforkmodulepath-args-options).
+Allow customizing all options passed to `child_process.fork`. By default, some values are set (`cwd`, `env`, `execArgv` and `serialization`), but you can override them and customize the rest. For a list of valid values, check [the Node documentation](https://nodejs.org/api/child_process.html#child_process_child_process_fork_modulepath_args_options).
 
 #### `maxRetries: number` (optional)
 

packages/jest-worker/src/workers/ChildProcessWorker.ts

@@ -92,6 +92,9 @@ export default class ChildProcessWorker implements WorkerInterface {
       },
       // Suppress --debug / --inspect flags while preserving others (like --harmony).
       execArgv: process.execArgv.filter(v => !/^--(debug|inspect)/.test(v)),
+      // default to advanced serialization in order to match worker threads
+      // @ts-expect-error: option does not exist on the node 12 types
+      serialization: 'advanced',
       silent: true,
       ...this._options.forkOptions,
     });

packages/jest-worker/src/workers/__tests__/ChildProcessWorker.test.js

@@ -70,6 +70,7 @@ it('passes fork options down to child_process.fork, adding the defaults', () =>
     env: {...process.env, FORCE_COLOR: supportsColor.stdout ? '1' : undefined}, // Default option.
     execArgv: ['-p'], // Filtered option.
     execPath: 'hello', // Added option.
+    serialization: 'advanced', // Default option.
     silent: true, // Default option.
   });
 });