fix: can mock non-existent paths and virtual modules via __mocks__

examples/mocks/__mocks__/virtual-module.ts

@@ -0,0 +1 @@
+export const value = 'folder'

examples/mocks/__mocks__/vscode-mocks.ts

@@ -0,0 +1 @@
+export const folder = true

examples/mocks/test/virtual.test.ts

@@ -0,0 +1,24 @@
+// @ts-expect-error vscode is not installed
+import * as vscodeMocks from 'vscode-mocks'
+// @ts-expect-error vscode is not installed
+import * as vscodeFactory from 'vscode-factory'
+// @ts-expect-error virtual module
+import * as virtual from 'virtual-module'
+
+vi.mock('vscode-mocks')
+vi.mock('vscode-factory', () => {
+  return { factory: true }
+})
+vi.mock('virtual-module')
+
+it('mocks not installed in mocks folder', () => {
+  expect(vscodeMocks.folder).toBe(true)
+})
+
+it('mocks not installed in mocks factory', () => {
+  expect(vscodeFactory.factory).toBe(true)
+})
+
+it('mocks virtual modules in mocks folder', () => {
+  expect(virtual.value).toBe('folder')
+})

examples/mocks/vite.config.ts

@@ -4,6 +4,22 @@ import { defineConfig } from 'vite'
 
 // https://vitejs.dev/config/
 export default defineConfig({
+  plugins: [
+    {
+      name: 'example',
+      resolveId(source) {
+        if (source === 'virtual-module')
+          return source
+      },
+      load(id) {
+        if (id === 'virtual-module') {
+          return `
+            export const value = 'original';
+          `
+        }
+      },
+    },
+  ],
   test: {
     globals: true,
     environment: 'node',

packages/vitest/src/runtime/mocker.ts

@@ -63,9 +63,13 @@ export class VitestMocker {
 
   private async resolvePath(id: string, importer: string) {
     const path = await this.options.resolveId!(id, importer)
+    // external is node_module or unresolved module
+    // for example, some people mock "vscode" and don't have it installed
+    const external = path == null || path.id.includes('/node_modules/') ? id : null
+
     return {
       path: normalizeRequestId(path?.id || id),
-      external: path?.id.includes('/node_modules/') ? id : null,
+      external,
     }
   }
 
@@ -115,15 +119,15 @@ export class VitestMocker {
 
     // it's a node_module alias
     // all mocks should be inside <root>/__mocks__
-    if (external || isNodeBuiltin(mockPath)) {
+    if (external || isNodeBuiltin(mockPath) || !existsSync(mockPath)) {
       const mockDirname = dirname(path) // for nested mocks: @vueuse/integration/useJwt
-      const baseFilename = basename(path)
       const mockFolder = resolve(this.root, '__mocks__', mockDirname)
 
       if (!existsSync(mockFolder))
         return null
 
       const files = readdirSync(mockFolder)
+      const baseFilename = basename(path)
 
       for (const file of files) {
         const [basename] = file.split('.')