feat: make libp2p a state machine (#257)

* docs: add events to readme

test/ping.node.js

@@ -0,0 +1,61 @@
+/* eslint-env mocha */
+'use strict'
+
+const chai = require('chai')
+chai.use(require('dirty-chai'))
+const expect = chai.expect
+const parallel = require('async/parallel')
+
+const createNode = require('./utils/create-node.js')
+const echo = require('./utils/echo')
+
+describe('ping', () => {
+  let nodeA
+  let nodeB
+
+  before((done) => {
+    parallel([
+      (cb) => createNode('/ip4/0.0.0.0/tcp/0', (err, node) => {
+        expect(err).to.not.exist()
+        nodeA = node
+        node.handle('/echo/1.0.0', echo)
+        node.start(cb)
+      }),
+      (cb) => createNode('/ip4/0.0.0.0/tcp/0', (err, node) => {
+        expect(err).to.not.exist()
+        nodeB = node
+        node.handle('/echo/1.0.0', echo)
+        node.start(cb)
+      })
+    ], done)
+  })
+
+  after((done) => {
+    parallel([
+      (cb) => nodeA.stop(cb),
+      (cb) => nodeB.stop(cb)
+    ], done)
+  })
+
+  it('should be able to ping another node', (done) => {
+    nodeA.ping(nodeB.peerInfo, (err, ping) => {
+      expect(err).to.not.exist()
+      ping.once('ping', (time) => {
+        expect(time).to.exist()
+        ping.stop()
+        done()
+      })
+
+      ping.start()
+    })
+  })
+
+  it('should be not be able to ping when stopped', (done) => {
+    nodeA.stop(() => {
+      nodeA.ping(nodeB.peerInfo, (err) => {
+        expect(err).to.exist()
+        done()
+      })
+    })
+  })
+})