add unittests for event-emitter

web/app/components/workflow/collaboration/core/__tests__/event-emitter.test.ts

@@ -0,0 +1,93 @@
+import { EventEmitter } from '../event-emitter'
+
+describe('EventEmitter', () => {
+  it('registers and invokes handlers via on/emit', () => {
+    const emitter = new EventEmitter()
+    const handler = jest.fn()
+
+    emitter.on('test', handler)
+    emitter.emit('test', { value: 42 })
+
+    expect(handler).toHaveBeenCalledWith({ value: 42 })
+  })
+
+  it('removes specific handler with off', () => {
+    const emitter = new EventEmitter()
+    const handlerA = jest.fn()
+    const handlerB = jest.fn()
+
+    emitter.on('test', handlerA)
+    emitter.on('test', handlerB)
+
+    emitter.off('test', handlerA)
+    emitter.emit('test', 'payload')
+
+    expect(handlerA).not.toHaveBeenCalled()
+    expect(handlerB).toHaveBeenCalledWith('payload')
+  })
+
+  it('clears all listeners when off is called without handler', () => {
+    const emitter = new EventEmitter()
+    const handlerA = jest.fn()
+    const handlerB = jest.fn()
+
+    emitter.on('trigger', handlerA)
+    emitter.on('trigger', handlerB)
+
+    emitter.off('trigger')
+    emitter.emit('trigger', 'payload')
+
+    expect(handlerA).not.toHaveBeenCalled()
+    expect(handlerB).not.toHaveBeenCalled()
+    expect(emitter.getListenerCount('trigger')).toBe(0)
+  })
+
+  it('removeAllListeners clears every registered event', () => {
+    const emitter = new EventEmitter()
+    emitter.on('one', jest.fn())
+    emitter.on('two', jest.fn())
+
+    emitter.removeAllListeners()
+
+    expect(emitter.getListenerCount('one')).toBe(0)
+    expect(emitter.getListenerCount('two')).toBe(0)
+  })
+
+  it('returns an unsubscribe function from on', () => {
+    const emitter = new EventEmitter()
+    const handler = jest.fn()
+
+    const unsubscribe = emitter.on('detach', handler)
+    unsubscribe()
+
+    emitter.emit('detach', 'value')
+
+    expect(handler).not.toHaveBeenCalled()
+  })
+
+  it('continues emitting when a handler throws', () => {
+    const emitter = new EventEmitter()
+    const errorHandler = jest
+      .spyOn(console, 'error')
+      .mockImplementation()
+
+    const failingHandler = jest.fn(() => {
+      throw new Error('boom')
+    })
+    const succeedingHandler = jest.fn()
+
+    emitter.on('safe', failingHandler)
+    emitter.on('safe', succeedingHandler)
+
+    emitter.emit('safe', 7)
+
+    expect(failingHandler).toHaveBeenCalledWith(7)
+    expect(succeedingHandler).toHaveBeenCalledWith(7)
+    expect(errorHandler).toHaveBeenCalledWith(
+      expect.stringContaining('Error in event handler for safe:'),
+      expect.any(Error),
+    )
+
+    errorHandler.mockRestore()
+  })
+})