add integration tests to validate piping to the CLI

integrations/tailwindcss-cli/tests/integration.test.js

@@ -1,3 +1,4 @@
+let { Readable } = require('stream')
 let $ = require('../../execute')
 let { css, html, javascript } = require('../../syntax')
 
@@ -10,6 +11,18 @@ function ready(message) {
   return message.includes('Done in')
 }
 
+class ReadableString extends Readable {
+  constructor(string) {
+    super()
+    this.data = string
+  }
+
+  _read() {
+    this.push(this.data)
+    this.push(null)
+  }
+}
+
 describe('static build', () => {
   it('should be possible to generate tailwind output', async () => {
     await writeInputFile('index.html', html`<div class="font-bold"></div>`)
@@ -27,6 +40,30 @@ describe('static build', () => {
     )
   })
 
+  it('should be possible to pipe in data', async () => {
+    await writeInputFile('index.html', html`<div class="font-bold"></div>`)
+
+    let initialCss = css`
+      @tailwind base;
+      @tailwind components;
+      @tailwind utilities;
+    `
+    let customStdin = new ReadableString(initialCss)
+
+    await $('node ../../lib/cli.js -o ./dist/main.css', {
+      stdio: [customStdin, 'pipe', 'pipe'],
+      env: { NODE_ENV: 'production' },
+    })
+
+    expect(await readOutputFile('main.css')).toIncludeCss(
+      css`
+        .font-bold {
+          font-weight: 700;
+        }
+      `
+    )
+  })
+
   it('should safelist a list of classes to always include', async () => {
     await writeInputFile('index.html', html`<div class="font-bold"></div>`)
     await writeInputFile(