chore: add pubsub example tests (#850)

examples/pubsub/message-filtering/test.js

@@ -0,0 +1,67 @@
+'use strict'
+
+const path = require('path')
+const execa = require('execa')
+const pDefer = require('p-defer')
+const uint8ArrayToString = require('uint8arrays/to-string')
+
+const stdout = [
+  {
+    topic: 'banana',
+    messageCount: 2
+  },
+  {
+    topic: 'apple',
+    messageCount: 2
+  },
+  {
+    topic: 'car',
+    messageCount: 0
+  },
+  {
+    topic: 'orange',
+    messageCount: 2
+  },
+]
+
+async function test () {
+  const defer = pDefer()
+  let topicCount = 0
+  let topicMessageCount = 0
+
+  process.stdout.write('message-filtering/1.js\n')
+
+  const proc = execa('node', [path.join(__dirname, '1.js')], {
+    cwd: path.resolve(__dirname),
+    all: true
+  })
+
+  proc.all.on('data', async (data) => {
+    // End
+    if (topicCount === stdout.length) {
+      defer.resolve()
+      proc.all.removeAllListeners('data')
+    }
+
+    process.stdout.write(data)
+    const line = uint8ArrayToString(data)
+
+    if (stdout[topicCount] && line.includes(stdout[topicCount].topic)) {
+      // Validate previous number of messages
+      if (topicCount > 0 && topicMessageCount > stdout[topicCount - 1].messageCount) {
+        defer.reject()
+        throw new Error(`topic ${stdout[topicCount - 1].topic} had ${topicMessageCount} messages instead of ${stdout[topicCount - 1].messageCount}`)
+      }
+
+      topicCount++
+      topicMessageCount = 0
+    } else {
+      topicMessageCount++
+    }
+  })
+
+  await defer.promise
+  proc.kill()
+}
+
+module.exports = test