Add tests for EventEmitter. (vercel#2515)

arunoda · web-flow · commit 871bc4e06b4c · 2017-07-09T09:16:53.000+05:30
diff --git a/lib/EventEmitter.js b/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)
   }
 }
diff --git a/test/unit/EventEmitter.test.js b/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)
+    })
+  })
+})

Original file line number	Diff line number	Diff line change
`@@ -6,6 +6,10 @@ export default class EventEmitter {`
`6`	`6`	`this.listeners[event] = new Set()`
`7`	`7`	`}`
`8`	`8`
	`9`	`+ if (this.listeners[event].has(cb)) {`
	`10`	+ throw new Error(`The listener already exising in event: ${event}`)
	`11`	`+ }`
	`12`	`+`
`9`	`13`	`this.listeners[event].add(cb)`
`10`	`14`	`}`
`11`	`15`
`@@ -15,7 +19,6 @@ export default class EventEmitter {`
`15`	`19`	`}`
`16`	`20`
`17`	`21`	`off (event, cb) {`
`18`		`- if (!this.listeners[event]) return`
`19`	`22`	`this.listeners[event].delete(cb)`
`20`	`23`	`}`
`21`	`24`	`}`