test(query-core/subscribable): add unit tests for 'Subscribable' base class

packages/query-core/src/__tests__/subscribable.test.tsx

@@ -0,0 +1,109 @@
+import { describe, expect, it, vi } from 'vitest'
+import { Subscribable } from '../subscribable'
+
+type Listener = () => void
+
+class SubscribableTest extends Subscribable<Listener> {
+  onSubscribeSpy = vi.fn()
+  onUnsubscribeSpy = vi.fn()
+
+  protected onSubscribe(): void {
+    this.onSubscribeSpy()
+  }
+
+  protected onUnsubscribe(): void {
+    this.onUnsubscribeSpy()
+  }
+}
+
+describe('Subscribable', () => {
+  it('should call onSubscribe when a listener subscribes', () => {
+    const subscribable = new SubscribableTest()
+
+    subscribable.subscribe(() => undefined)
+
+    expect(subscribable.onSubscribeSpy).toHaveBeenCalledTimes(1)
+    expect(subscribable.onUnsubscribeSpy).toHaveBeenCalledTimes(0)
+  })
+
+  it('should call onSubscribe once per subscribe call', () => {
+    const subscribable = new SubscribableTest()
+
+    subscribable.subscribe(() => undefined)
+    subscribable.subscribe(() => undefined)
+
+    expect(subscribable.onSubscribeSpy).toHaveBeenCalledTimes(2)
+  })
+
+  it('should call onUnsubscribe when a listener unsubscribes', () => {
+    const subscribable = new SubscribableTest()
+
+    const unsubscribe = subscribable.subscribe(() => undefined)
+    unsubscribe()
+
+    expect(subscribable.onUnsubscribeSpy).toHaveBeenCalledTimes(1)
+  })
+
+  it('should return `false` from hasListeners when there are no listeners', () => {
+    const subscribable = new SubscribableTest()
+
+    expect(subscribable.hasListeners()).toBe(false)
+  })
+
+  it('should return `true` from hasListeners while a listener is subscribed', () => {
+    const subscribable = new SubscribableTest()
+
+    subscribable.subscribe(() => undefined)
+
+    expect(subscribable.hasListeners()).toBe(true)
+  })
+
+  it('should return `false` from hasListeners after the last listener unsubscribes', () => {
+    const subscribable = new SubscribableTest()
+
+    const unsubscribe = subscribable.subscribe(() => undefined)
+    unsubscribe()
+
+    expect(subscribable.hasListeners()).toBe(false)
+  })
+
+  it('should still have listeners while at least one remains subscribed', () => {
+    const subscribable = new SubscribableTest()
+
+    const unsubscribe1 = subscribable.subscribe(() => undefined)
+    subscribable.subscribe(() => undefined)
+
+    unsubscribe1()
+
+    expect(subscribable.hasListeners()).toBe(true)
+  })
+
+  it('should deduplicate the same listener reference', () => {
+    const subscribable = new SubscribableTest()
+    const listener = () => undefined
+
+    subscribable.subscribe(listener)
+    subscribable.subscribe(listener)
+
+    expect(subscribable.hasListeners()).toBe(true)
+
+    const unsubscribe = subscribable.subscribe(listener)
+    unsubscribe()
+
+    expect(subscribable.hasListeners()).toBe(false)
+  })
+
+  it('should keep a stable subscribe reference when destructured', () => {
+    const subscribable = new SubscribableTest()
+    const { subscribe } = subscribable
+
+    const unsubscribe = subscribe(() => undefined)
+
+    expect(subscribable.onSubscribeSpy).toHaveBeenCalledTimes(1)
+    expect(subscribable.hasListeners()).toBe(true)
+
+    unsubscribe()
+
+    expect(subscribable.hasListeners()).toBe(false)
+  })
+})