wow! crazy how much work that took

src/compiler/config/test/load-config.spec.ts

@@ -1,7 +1,8 @@
+import { getMockFSPatch } from '@stencil/core/testing';
 import { createNodeSys } from '@sys-api-node';
-import path from 'path';
-import mock from 'mock-fs';
 import fs from 'fs';
+import mock from 'mock-fs';
+import path from 'path';
 
 import { ConfigFlags } from '../../../cli/config-flags';
 import type * as d from '../../../declarations';
@@ -41,6 +42,7 @@ describe('load config', () => {
       [configPath2]: mock.load(path.resolve(__dirname, configPath2)),
       'fixtures/tsconfig.json': tsconfig,
       [noTsConfigPath]: mock.load(path.resolve(__dirname, configPath)),
+      ...getMockFSPatch(mock),
     });
   });
 
@@ -101,10 +103,7 @@ describe('load config', () => {
     });
 
     it('creates a tsconfig file when "initTsConfig" set', async () => {
-      const tsconfigPath = path.resolve(
-        path.dirname(noTsConfigPath),
-        "tsconfig.json"
-      );
+      const tsconfigPath = path.resolve(path.dirname(noTsConfigPath), 'tsconfig.json');
       expect(fs.existsSync(tsconfigPath)).toBe(false);
       const loadedConfig = await loadConfig({ initTsConfig: true, configPath: noTsConfigPath });
       expect(fs.existsSync(tsconfigPath)).toBe(true);

src/compiler/config/test/validate-config-sourcemap.spec.ts

@@ -1,15 +1,15 @@
 import { mockLoadConfigInit } from '@stencil/core/testing';
+import { getMockFSPatch } from '@stencil/core/testing';
 import { createNodeSys } from '@sys-api-node';
-import path from 'path';
 import mock from 'mock-fs';
-import fs from 'fs';
+import path from 'path';
 
 import type * as d from '../../../declarations';
 import { loadConfig } from '../load-config';
 
 describe('stencil config - sourceMap option', () => {
   const fixturesDir = 'fixtures';
-  const configPath = path.join(fixturesDir, "stencil.config.ts");
+  const configPath = path.join(fixturesDir, 'stencil.config.ts');
   let sys: d.CompilerSystem;
 
   /**
@@ -35,14 +35,14 @@ describe('stencil config - sourceMap option', () => {
 
     mock({
       [configPath]: mock.load(path.resolve(__dirname, configPath)),
+      ...getMockFSPatch(mock),
     });
   });
 
   afterEach(() => {
     mock.restore();
   });
 
-
   it('sets sourceMap options to true in tsconfig', async () => {
     const testConfig = getLoadConfigForTests({ config: { sourceMap: true } });
 

src/testing/index.ts

@@ -27,5 +27,5 @@ export { E2EElement, E2EPage, newE2EPage } from './puppeteer';
 export { newSpecPage } from './spec-page';
 export { transpile } from './test-transpile';
 export { createTesting } from './testing';
-export { shuffleArray } from './testing-utils';
+export { getMockFSPatch, shuffleArray } from './testing-utils';
 export type { EventSpy, SpecPage, Testing } from '@stencil/core/internal';

src/testing/testing-utils.ts

@@ -1,6 +1,6 @@
 import type * as d from '@stencil/core/internal';
 import { isOutputTargetDistLazy, isOutputTargetWww } from '@utils';
-import { join, relative } from 'path';
+import path, { join, relative } from 'path';
 
 import { InMemoryFileSystem } from '../compiler/sys/in-memory-fs';
 
@@ -191,3 +191,25 @@ export async function withSilentWarn<T>(cb: SilentWarnFunc<T>): Promise<T> {
   console.warn = realWarn;
   return retVal;
 }
+
+/**
+ * This is our custom patched version of `mock-fs`. This replaces the node.js
+ * implementation of `fs` with a separate one which does filesystem operations
+ * against an in-memory filesystem instead of against the disk.
+ *
+ * The 'patch' consists of adding files to the in-memory filesystem from the
+ * disk which are sometimes required by Jest between the `beforeEach` and
+ * `afterEach` calls in a test suite -- without adding these files to the
+ * in-memory filesystem the runtime require by Jest will fail.
+ *
+ * @param mock a `mock-fs` module, as imported in the particular test file
+ * where you want to mock the filesystem.
+ * @returns a filesystem manifest suitable for mocking out runtime
+ * dependencies of Jest
+ */
+export const getMockFSPatch = (mock: any) => ({
+  'node_modules/write-file-atomic': mock.load(path.resolve(process.cwd(), 'node_modules', 'write-file-atomic')),
+  'node_modules/imurmurhash': mock.load(path.resolve(process.cwd(), 'node_modules', 'imurmurhash')),
+  'node_modules/is-typedarray': mock.load(path.resolve(process.cwd(), 'node_modules', 'is-typedarray')),
+  'node_modules/typedarray-to-buffer': mock.load(path.resolve(process.cwd(), 'node_modules', 'typedarray-to-buffer')),
+});