Fixing Async Timing Tests In UseDraftRecovery.test.ts
Hey everyone! Let's dive into the nitty-gritty of debugging and fixing those pesky skipped tests in our useDraftRecovery.test.ts
file. Specifically, we're tackling two async timing tests that have been giving us a headache. This isn't just about getting the test suite to pass; it’s about ensuring our code is robust and reliable.
Summary of the Issue
Okay, so here's the deal. We have a couple of tests in useDraftRecovery.test.ts
that are being skipped. These tests are crucial because they validate the discard()
function, which is an async operation. Currently, 12 out of 14 tests are passing—that's a solid 85%—but we can't ignore those remaining 15%. It’s like having a nearly perfect pizza but with two slices missing!
Passing Tests (12/14 or 85%):
- ✅ Recovery prompt detection
- ✅ localStorage draft comparison
- ✅ DB draft fetching
- ✅ Recover action
- ✅ Error handling
- ✅ Timestamp comparison
- ✅ Full recovery flow
Skipped Tests (2/14 or 15%):
- ⏭️
loads DB draft after discard if it exists
- ⏭️
completes full discard flow: detect → discard → use DB draft
Diving Deeper into the Root Cause
The core issue revolves around the discard()
function. This function is async, meaning it doesn't execute instantaneously. It calls getDraftByContact()
to fetch the database draft after removing the local storage draft. Our mocking setup uses mockResolvedValueOnce()
, which works perfectly for the initial call during the hook initialization. However, the second call during discard()
stubbornly returns null, even though it's supposed to be properly mocked.
We've tried a bunch of fixes already:
- ✅ Fixed the Supabase authentication mock. Authentication is key, guys, and we wanted to rule this out.
- ✅ Switched from a wrapper function to direct mocking. Sometimes, simpler is better.
- ✅ Added
await act(async () => { await discard() })
. This was to ensure we're waiting for all the async operations to complete. React'sact
is super useful for this. - ✅ Used
.mockResolvedValueOnce().mockResolvedValueOnce()
for handling multiple calls. We thought maybe we needed to explicitly mock each call. - ❌ But, alas, it's still failing! The mock is still returning null on that second call.
The good news? We're pretty sure these are test environment timing issues, not actual bugs in our production code. Phew! Still, we need to nail this.
How to Reproduce the Issue
Want to see the problem for yourself? Here’s how you can reproduce it:
cd apps/web
pnpm test hooks/useDraftRecovery.test.ts
Expected Result: All 14 tests should pass, green across the board!
Actual Result: 12 pass, but those 2 are stubbornly skipped.
Next Steps: Let's Get This Sorted
Alright, so we’ve identified the problem and know how to reproduce it. Now, let's talk about our next moves.
- Investigate Jest Mock Behavior with Async State Updates: We need to understand how Jest's mocking mechanism plays with async state updates in React hooks. There might be some nuances we're missing.
- Try
mockImplementation
Instead ofmockResolvedValue
:mockImplementation
gives us more control. Instead of just returning a resolved value, we can define a function to be executed. This might help us better simulate the async behavior we're expecting. - Consider Using
renderHook
with a Custom Wrapper: UsingrenderHook
with a custom wrapper can provide a more stable mock context. This involves creating a component that wraps the hook and provides the necessary context, which can help isolate the hook's behavior in the test environment. - Test with a Real Supabase Test Environment: Mocks are great, but sometimes nothing beats testing against the real thing. Setting up a dedicated Supabase test environment could help us catch timing issues that mocks might miss.
Deep Dive into Jest Mocking and Async Behavior
Understanding Jest's mocking behavior, especially in asynchronous scenarios, is crucial for writing reliable tests. Jest's mockResolvedValue
and mockResolvedValueOnce
are handy tools, but they can sometimes fall short when dealing with complex timing issues in React hooks. The problem often lies in how React's state updates interact with the mocked asynchronous functions.
When a React hook involves asynchronous operations, such as fetching data from a database or an API, the state updates triggered by these operations might not be immediately reflected in the test environment. This is because React's state updates are batched and processed asynchronously. As a result, when you mock an async function and use mockResolvedValueOnce
, the mocked value might not be available when the hook's internal logic expects it, especially if the function is called multiple times within a short period.
For example, in our case with useDraftRecovery
, the discard()
function triggers an async operation that fetches data from the database after removing a local storage draft. The first call to getDraftByContact()
during hook initialization works fine because the mocked value is available. However, the second call within discard()
might occur before the mocked value for the second call is set up, leading to a null return.
To address this, we need to explore more robust mocking techniques. One promising approach is using mockImplementation
. Unlike mockResolvedValue
, which simply returns a predefined value, mockImplementation
allows us to define a custom function that mimics the behavior of the original async function. This gives us finer-grained control over the timing and sequence of mocked responses.
For instance, we can use mockImplementation
to simulate delays or conditional responses, ensuring that the mocked function behaves more realistically in the context of our hook. This can help us catch race conditions or timing-related bugs that might be missed by simpler mocking methods.
Another technique is to use jest.advanceTimersByTime
to control the execution of timers in our tests. This can be particularly useful when dealing with setTimeout
or setInterval
within the hook. By advancing the timers, we can ensure that the necessary asynchronous operations are triggered and completed in the expected order.
Additionally, using renderHook
with a custom wrapper can provide a more isolated and controlled testing environment. The custom wrapper can set up the necessary context and mock providers, ensuring that the hook receives the dependencies it expects. This can help prevent issues caused by external dependencies interfering with the hook's behavior.
By thoroughly investigating these mocking techniques and their interaction with React's asynchronous state updates, we can better understand and resolve the timing issues in our tests.
The Power of mockImplementation
Let's zoom in on mockImplementation
a bit more. This method is a powerhouse when it comes to crafting realistic mock behaviors. Instead of just saying,