test(query-core): add unit tests for thenable

Author: sobol-sudo

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

@@ -0,0 +1,112 @@
+import { describe, expect, it, vi } from 'vitest'
+import { pendingThenable, tryResolveSync } from '../thenable'
+import type { FulfilledThenable, RejectedThenable } from '../thenable'
+
+describe('pendingThenable', () => {
+  it('should start out pending with resolve and reject attached', () => {
+    const thenable = pendingThenable<string>()
+
+    expect(thenable.status).toBe('pending')
+    expect(typeof thenable.resolve).toBe('function')
+    expect(typeof thenable.reject).toBe('function')
+  })
+
+  it('should expose the value and drop the pending props once resolved', async () => {
+    const thenable = pendingThenable<string>()
+
+    thenable.resolve('data')
+
+    expect(thenable.status).toBe('fulfilled')
+    expect((thenable as unknown as FulfilledThenable<string>).value).toBe('data')
+    expect(thenable.resolve).toBeUndefined()
+    expect(thenable.reject).toBeUndefined()
+    await expect(thenable).resolves.toBe('data')
+  })
+
+  it('should expose the reason and drop the pending props once rejected', async () => {
+    const thenable = pendingThenable<string>()
+    const reason = new Error('error')
+
+    thenable.reject(reason)
+
+    expect(thenable.status).toBe('rejected')
+    expect((thenable as unknown as RejectedThenable<string>).reason).toBe(reason)
+    expect(thenable.resolve).toBeUndefined()
+    expect(thenable.reject).toBeUndefined()
+    await expect(thenable).rejects.toBe(reason)
+  })
+
+  it('should not reject a second time after being resolved', async () => {
+    const thenable = pendingThenable<string>()
+
+    thenable.resolve('data')
+    // `reject` is deleted on finalize, so a late caller cannot settle it twice
+    expect(thenable.reject).toBeUndefined()
+
+    await expect(thenable).resolves.toBe('data')
+  })
+
+  it('should not report an unhandled rejection when nobody awaits it', async () => {
+    const onUnhandledRejection = vi.fn()
+    process.on('unhandledRejection', onUnhandledRejection)
+
+    pendingThenable<string>().reject(new Error('error'))
+    // unhandled rejections are reported after the microtask queue drains
+    await new Promise((resolve) => setTimeout(resolve, 0))
+
+    process.off('unhandledRejection', onUnhandledRejection)
+    expect(onUnhandledRejection).not.toHaveBeenCalled()
+  })
+})
+
+describe('tryResolveSync', () => {
+  it('should return undefined for an already resolved native promise', () => {
+    // `then` on a native promise always defers to a microtask, so the data is
+    // never synchronously available
+    expect(tryResolveSync(Promise.resolve('data'))).toBeUndefined()
+  })
+
+  it('should return the data of a thenable that resolves synchronously', () => {
+    const thenable = {
+      then: (onFulfilled: (value: string) => unknown) => {
+        onFulfilled('data')
+        return Promise.resolve('data')
+      },
+    } as unknown as Promise<string>
+
+    expect(tryResolveSync(thenable)).toEqual({ data: 'data' })
+  })
+
+  it('should support a synchronous thenable whose then() has no catch', () => {
+    // a React thenable is not always a full promise, so `then` may return
+    // something without a `catch` method
+    const thenable = {
+      then: (onFulfilled: (value: string) => unknown) => {
+        onFulfilled('data')
+      },
+    } as unknown as Promise<string>
+
+    expect(tryResolveSync(thenable)).toEqual({ data: 'data' })
+  })
+
+  it('should return undefined when a synchronous thenable resolves with undefined', () => {
+    const thenable = {
+      then: (onFulfilled: (value: undefined) => unknown) => {
+        onFulfilled(undefined)
+      },
+    } as unknown as Promise<undefined>
+
+    expect(tryResolveSync(thenable)).toBeUndefined()
+  })
+
+  it('should return undefined for a rejected promise without leaving it unhandled', async () => {
+    const onUnhandledRejection = vi.fn()
+    process.on('unhandledRejection', onUnhandledRejection)
+
+    expect(tryResolveSync(Promise.reject(new Error('error')))).toBeUndefined()
+    await new Promise((resolve) => setTimeout(resolve, 0))
+
+    process.off('unhandledRejection', onUnhandledRejection)
+    expect(onUnhandledRejection).not.toHaveBeenCalled()
+  })
+})