Add tests for EventEmitter. (#2515)

lib/EventEmitter.js

@@ -6,6 +6,10 @@ export default class EventEmitter {
       this.listeners[event] = new Set()
     }
 
+    if (this.listeners[event].has(cb)) {
+      throw new Error(`The listener already exising in event: ${event}`)
+    }
+
     this.listeners[event].add(cb)
   }
 
@@ -15,7 +19,6 @@ export default class EventEmitter {
   }
 
   off (event, cb) {
-    if (!this.listeners[event]) return
     this.listeners[event].delete(cb)
   }
 }

test/unit/EventEmitter.test.js

@@ -0,0 +1,82 @@
+/* global describe, it, expect */
+import EventEmitter from '../../dist/lib/EventEmitter'
+
+describe('EventEmitter', () => {
+  describe('With listeners', () => {
+    it('should listen to a event', (done) => {
+      const ev = new EventEmitter()
+      ev.on('sample', done)
+      ev.emit('sample')
+    })
+
+    it('should listen to multiple listeners', () => {
+      const ev = new EventEmitter()
+      let cnt = 0
+
+      ev.on('sample', () => { cnt += 1 })
+      ev.on('sample', () => { cnt += 1 })
+
+      ev.emit('sample')
+
+      expect(cnt).toBe(2)
+    })
+
+    it('should listen to multiple events', () => {
+      const ev = new EventEmitter()
+      const data = []
+      const cb = (name) => { data.push(name) }
+
+      ev.on('sample1', cb)
+      ev.on('sample2', cb)
+
+      ev.emit('sample1', 'one')
+      ev.emit('sample2', 'two')
+
+      expect(data).toEqual(['one', 'two'])
+    })
+
+    it('should support multiple arguments', () => {
+      const ev = new EventEmitter()
+      let data
+
+      ev.on('sample', (...args) => { data = args })
+      ev.emit('sample', 'one', 'two')
+
+      expect(data).toEqual(['one', 'two'])
+    })
+
+    it('should possible to stop listening an event', () => {
+      const ev = new EventEmitter()
+      let cnt = 0
+      const cb = () => { cnt += 1 }
+
+      ev.on('sample', cb)
+
+      ev.emit('sample')
+      expect(cnt).toBe(1)
+
+      ev.off('sample', cb)
+
+      ev.emit('sample')
+      expect(cnt).toBe(1)
+    })
+
+    it('should throw when try to add the same listener multiple times', () => {
+      const ev = new EventEmitter()
+      const cb = () => {}
+
+      ev.on('sample', cb)
+
+      const run = () => ev.on('sample', cb)
+
+      expect(run).toThrow(/The listener already exising in event: sample/)
+    })
+  })
+
+  describe('Without a listener', () => {
+    it('should not fail to emit', () => {
+      const ev = new EventEmitter()
+      ev.emit('aaaa', 10, 20)
+    })
+  })
+})