test_runner: add mock file system support

Author: sozua

lib/internal/test_runner/mock/mock.js

@@ -48,10 +48,12 @@ const {
   validateOneOf,
 } = require('internal/validators');
 const { MockTimers } = require('internal/test_runner/mock/mock_timers');
+const { MockFileSystem } = require('internal/test_runner/mock/mock_file_system');
 const { Module } = require('internal/modules/cjs/loader');
 const { _load, _nodeModulePaths, _resolveFilename, isBuiltin } = Module;
 function kDefaultFunction() {}
 const enableModuleMocking = getOptionValue('--experimental-test-module-mocks');
+const enableFsMocking = getOptionValue('--experimental-test-fs-mocks');
 const kSupportedFormats = [
   'builtin',
   'commonjs-typescript',
@@ -405,6 +407,7 @@ const { restore: restoreProperty } = MockPropertyContext.prototype;
 class MockTracker {
   #mocks = [];
   #timers;
+  #fs;
 
   /**
    * Returns the mock timers of this MockTracker instance.
@@ -415,6 +418,21 @@ class MockTracker {
     return this.#timers;
   }
 
+  /**
+   * Returns the mock file system of this MockTracker instance.
+   * @returns {MockFileSystem} The mock file system instance.
+   */
+  get fs() {
+    if (!enableFsMocking) {
+      throw new ERR_INVALID_STATE(
+        'File system mocking is not enabled. ' +
+        'Use --experimental-test-fs-mocks to enable it.',
+      );
+    }
+    this.#fs ??= new MockFileSystem();
+    return this.#fs;
+  }
+
   /**
    * Creates a mock function tracker.
    * @param {Function} [original] - The original function to be tracked.
@@ -731,6 +749,7 @@ class MockTracker {
   reset() {
     this.restoreAll();
     this.#timers?.reset();
+    this.#fs?.reset();
     this.#mocks = [];
   }