chore: Add VeryShortWatchError typed error

- Add a new VeryShortWatchError struct for error matching, returned
  by `handleAnyWatch`, up through `Reflector.ListAndWatch`.
- Update test expectations to match exact errors.

Author: karlkfi

staging/src/k8s.io/client-go/tools/cache/reflector.go

@@ -960,7 +960,7 @@ loop:
 
 	watchDuration := clock.Since(start)
 	if watchDuration < 1*time.Second && eventCount == 0 {
-		return watchListBookmarkReceived, fmt.Errorf("very short watch: %s: Unexpected watch close - watch lasted less than a second and no items received", name)
+		return watchListBookmarkReceived, &VeryShortWatchError{Name: name}
 	}
 	klog.FromContext(ctx).V(4).Info("Watch close", "reflector", name, "type", expectedTypeName, "totalItems", eventCount)
 	return watchListBookmarkReceived, nil
@@ -1162,3 +1162,16 @@ type noopTicker struct{}
 func (t *noopTicker) C() <-chan time.Time { return nil }
 
 func (t *noopTicker) Stop() {}
+
+// VeryShortWatchError is returned when the watch result channel is closed
+// within one second, without having sent any events.
+type VeryShortWatchError struct {
+	// Name of the Reflector
+	Name string
+}
+
+// Error implements the error interface
+func (e *VeryShortWatchError) Error() string {
+	return fmt.Sprintf("very short watch: %s: Unexpected watch close - "+
+		"watch lasted less than a second and no items received", e.Name)
+}

staging/src/k8s.io/client-go/tools/cache/reflector_test.go

@@ -291,8 +291,7 @@ func TestReflectorHandleWatchResultChanClosedBefore(t *testing.T) {
 	// Simulate the result channel being closed by the producer before handleWatch is called.
 	close(resultCh)
 	err := handleWatch(ctx, time.Now(), fw, s, g.expectedType, g.expectedGVK, g.name, g.typeDescription, g.setLastSyncResourceVersion, g.clock, nevererrc)
-	// TODO(karlkfi): Add exact error type for "very short watch"
-	require.Error(t, err)
+	require.Equal(t, &VeryShortWatchError{Name: g.name}, err)
 	// Ensure handleWatch calls ResultChan and Stop
 	assert.Equal(t, []string{"ResultChan", "Stop"}, calls)
 }
@@ -323,8 +322,7 @@ func TestReflectorHandleWatchResultChanClosedAfter(t *testing.T) {
 		},
 	}
 	err := handleWatch(ctx, time.Now(), fw, s, g.expectedType, g.expectedGVK, g.name, g.typeDescription, g.setLastSyncResourceVersion, g.clock, nevererrc)
-	// TODO(karlkfi): Add exact error type for "very short watch"
-	require.Error(t, err)
+	require.Equal(t, &VeryShortWatchError{Name: g.name}, err)
 	// Ensure handleWatch calls ResultChan and Stop
 	assert.Equal(t, []string{"ResultChan", "Stop"}, calls)
 }