[v10] reduce sensitivity of fncache cancellation test

lib/utils/fncache_test.go

@@ -151,35 +151,48 @@ func testFnCacheSimple(t *testing.T, ttl time.Duration, delay time.Duration) {
 // in-progress loading continues, and the entry is correctly updated, even if the call to Get
 // which happened to trigger the load needs to be unblocked early.
 func TestFnCacheCancellation(t *testing.T) {
-	const timeout = time.Millisecond * 10
+	t.Parallel()
+
+	const longTimeout = time.Second * 10 // should never be hit
 
 	cache, err := NewFnCache(FnCacheConfig{TTL: time.Minute})
 	require.NoError(t, err)
 
-	ctx, cancel := context.WithTimeout(context.Background(), timeout)
-	defer cancel()
-
+	// used to artificially block the load function
 	blocker := make(chan struct{})
 
+	// set up a context that we can cancel from within the load function to
+	// simulate a scenario where the calling context is canceled or times out.
+	// if we actually hit the timeout, that is a bug.
+	ctx, cancel := context.WithTimeout(context.Background(), longTimeout)
+	defer cancel()
+
 	v, err := cache.Get(ctx, "key", func(context.Context) (interface{}, error) {
+		cancel()
 		<-blocker
 		return "val", nil
 	})
 
 	require.Nil(t, v)
-	require.Equal(t, context.DeadlineExceeded, trace.Unwrap(err))
+	require.Equal(t, context.Canceled, trace.Unwrap(err), "context should have been canceled immediately")
 
 	// unblock the loading operation which is still in progress
 	close(blocker)
 
-	ctx, cancel = context.WithTimeout(context.Background(), timeout)
+	// since we unblocked the loadfn, we expect the next Get to return almost
+	// immediately.  we still use a fairly long timeout just to ensure that failure
+	// is due to an actual bug and not due to resource constraints in the test env.
+	ctx, cancel = context.WithTimeout(context.Background(), longTimeout)
 	defer cancel()
 
+	loadFnWasRun := atomic.NewBool(false)
 	v, err = cache.Get(ctx, "key", func(context.Context) (interface{}, error) {
-		t.Fatal("this should never run!")
+		loadFnWasRun.Store(true)
 		return nil, nil
 	})
 
+	require.False(t, loadFnWasRun.Load(), "loadfn should not have been run")
+
 	require.NoError(t, err)
 	require.Equal(t, "val", v.(string))
 }