test coverage for js watch output to stdout

scripts/js-api-tests.js

@@ -6806,6 +6806,107 @@ let childProcessTests = {
       testKeepAlivePingPromise,
     ])
   },
+
+  async testWatchStdoutChildProcess({ testDir, esbuild }) {
+    const sequence = [
+      {
+        input: 'console.log(1+2)',
+        stdout: ['console.log(1 + 2);'],
+        stderr: ['[watch] build finished, watching for changes...'],
+      },
+      {
+        input: 'console.log(2+3)',
+        stdout: ['console.log(2 + 3);'],
+        stderr: ['[watch] build started (change: "in.js")', '[watch] build finished'],
+      },
+      {
+        input: 'console.log(3+4)',
+        stdout: ['console.log(3 + 4);'],
+        stderr: ['[watch] build started (change: "in.js")', '[watch] build finished'],
+      },
+    ]
+
+    const infile = path.join(testDir, 'in.js')
+    const file = path.join(testDir, 'build.js')
+    await writeFileAsync(infile, sequence[0].input)
+    await writeFileAsync(file, `
+      const esbuild = require(${JSON.stringify(esbuild.ESBUILD_PACKAGE_PATH)})
+      esbuild.context({
+        entryPoints: [${JSON.stringify(infile)}],
+        logLevel: 'info',
+      }).then(ctx => ctx.watch())
+    `)
+
+    // Start the child
+    const maxSeconds = 60
+    const child = child_process.spawn('node', [file], {
+      cwd: testDir,
+      stdio: ['inherit', 'pipe', 'pipe'],
+      timeout: maxSeconds * 1000,
+    })
+
+    // Make sure the child is always killed
+    try {
+      for (const { input, stdout: expectedStdout, stderr: expectedStderr } of sequence) {
+        let totalStdout = ''
+        let totalStderr = ''
+        let stdoutBuffer = ''
+        let stderrBuffer = ''
+        const onstdout = data => {
+          totalStdout += data
+          stdoutBuffer += data
+          check()
+        }
+        const onstderr = data => {
+          totalStderr += data
+          stderrBuffer += data
+          check()
+        }
+        let check = () => { }
+
+        child.stdout.on('data', onstdout)
+        child.stderr.on('data', onstderr)
+
+        await new Promise((resolve, reject) => {
+          const seconds = 30
+          const timeout = setTimeout(() => reject(new Error(
+            `Watch mode + stdout test failed to match expected output after ${seconds} seconds
+  input: ${JSON.stringify(input)}
+  stdout: ${JSON.stringify(totalStdout)}
+  stderr: ${JSON.stringify(totalStderr)}
+`)), seconds * 1000)
+
+          check = () => {
+            let index
+
+            while ((index = stdoutBuffer.indexOf('\n')) >= 0) {
+              const line = stdoutBuffer.slice(0, index)
+              stdoutBuffer = stdoutBuffer.slice(index + 1)
+              if (line === expectedStdout[0]) expectedStdout.shift()
+            }
+
+            while ((index = stderrBuffer.indexOf('\n')) >= 0) {
+              const line = stderrBuffer.slice(0, index)
+              stderrBuffer = stderrBuffer.slice(index + 1)
+              if (line === expectedStderr[0]) expectedStderr.shift()
+            }
+
+            if (!expectedStdout.length && !expectedStderr.length) {
+              clearTimeout(timeout)
+              resolve()
+            }
+          }
+
+          writeFileAtomic(infile, input)
+        })
+
+        child.stdout.off('data', onstdout)
+        child.stderr.off('data', onstderr)
+      }
+    } finally {
+      child.kill()
+    }
+  },
 }
 
 async function assertSourceMap(jsSourceMap, source) {