feat: add feature plugin tests and validation for feature flags

vite-layers/test/public.test.ts

@@ -1,6 +1,8 @@
 import { fileURLToPath } from 'node:url'
-import { dirname, resolve } from 'node:path'
-import { describe, expect, it } from 'vitest'
+import { mkdtempSync, readFileSync, readdirSync, rmSync } from 'node:fs'
+import { dirname, join, resolve } from 'node:path'
+import { tmpdir } from 'node:os'
+import { afterEach, beforeEach, describe, expect, it } from 'vitest'
 import { publicLayersPlugin } from '../src/public'
 
 const here = dirname(fileURLToPath(import.meta.url))
@@ -8,30 +10,65 @@ const fixture = (p: string) => resolve(here, 'fixtures', p)
 
 const callConfig = (p: { config?: unknown }) => (p.config as () => unknown)()
 
-function runGenerateBundle(p: { generateBundle?: unknown }): Record<string, string> {
-  const emitted: Record<string, string> = {}
-  const ctx = {
-    emitFile: ({ fileName, source }: { fileName: string; source: Buffer | string }) => {
-      emitted[fileName] = source.toString()
-    },
+type ResolvedishConfig = { root: string; build: { outDir: string; copyPublicDir?: boolean } }
+
+/** List every file written under `dir` as `posixRelativePath → contents`. */
+function snapshot(dir: string): Record<string, string> {
+  const out: Record<string, string> = {}
+  const walk = (d: string) => {
+    for (const name of readdirSync(d, { withFileTypes: true })) {
+      const abs = join(d, name.name)
+      if (name.isDirectory()) walk(abs)
+      else out[resolve(abs).slice(resolve(dir).length + 1).replace(/\\/g, '/')] = readFileSync(abs, 'utf8')
+    }
   }
-  ;(p.generateBundle as (this: unknown, ...a: unknown[]) => void).call(ctx, {}, {}, false)
-  return emitted
+  walk(dir)
+  return out
+}
+
+/** Drive the build-time hooks (configResolved → writeBundle) and return what landed on disk. */
+function runBuild(
+  p: { configResolved?: unknown; writeBundle?: unknown },
+  outDir: string,
+  { copyPublicDir, writeDir }: { copyPublicDir?: boolean; writeDir?: string } = {},
+): Record<string, string> {
+  const cfg: ResolvedishConfig = { root: '/', build: { outDir, copyPublicDir } }
+  ;(p.configResolved as (c: ResolvedishConfig) => void)(cfg)
+  ;(p.writeBundle as (this: unknown, o: { dir?: string }) => void).call({}, { dir: writeDir ?? outDir })
+  return snapshot(outDir)
 }
 
 describe('publicLayersPlugin', () => {
   const high = fixture('public/high/public')
   const low = fixture('public/low/public')
+  let outDir: string
+
+  beforeEach(() => {
+    outDir = mkdtempSync(join(tmpdir(), 'vite-layers-public-'))
+  })
+  afterEach(() => {
+    rmSync(outDir, { recursive: true, force: true })
+  })
 
   it('disables Vite publicDir when layers have public/, otherwise no-op', () => {
     expect(callConfig(publicLayersPlugin([high, low]))).toEqual({ publicDir: false })
     expect(callConfig(publicLayersPlugin([fixture('public/none/public')]))).toBeUndefined()
   })
 
-  it('emits assets first-match-wins (higher overrides, lower fills gaps, nested ok)', () => {
-    const emitted = runGenerateBundle(publicLayersPlugin([high, low]))
-    expect(emitted['logo.svg']).toBe('HIGH_LOGO') // overridden by the higher layer
-    expect(emitted['shared.txt']).toBe('LOW_SHARED') // inherited from the lower layer
-    expect(emitted['img/icon.svg']).toBe('LOW_ICON') // nested, from the lower layer
+  it('copies assets first-match-wins (higher overrides, lower fills gaps, nested ok)', () => {
+    const written = runBuild(publicLayersPlugin([high, low]), outDir)
+    expect(written['logo.svg']).toBe('HIGH_LOGO') // overridden by the higher layer
+    expect(written['shared.txt']).toBe('LOW_SHARED') // inherited from the lower layer
+    expect(written['img/icon.svg']).toBe('LOW_ICON') // nested, from the lower layer
+  })
+
+  it('skips the copy when Vite opts out (copyPublicDir: false)', () => {
+    const written = runBuild(publicLayersPlugin([high, low]), outDir, { copyPublicDir: false })
+    expect(written).toEqual({})
+  })
+
+  it('only copies for the output targeting the main outDir', () => {
+    const written = runBuild(publicLayersPlugin([high, low]), outDir, { writeDir: join(outDir, 'server') })
+    expect(written).toEqual({})
   })
 })