actor/test: extend TestAwaitFuture to cover fn.Err result path

Roasbeef · Roasbeef · commit fb86988c4ec2 · 2026-04-10T19:16:49.000-07:00
In this commit, we extend TestAwaitFuture to cover the case where the
future is completed with an fn.Err result. The existing test only
exercised the fn.Ok (success) and context cancellation paths.

The new case calls promise.Complete(fn.Err[string](sentinel)) directly
and verifies that AwaitFuture surfaces the error as the second return
value while returning the zero string value in the first, which is the
documented contract for Result[T].Unpack().
diff --git a/actor/future_test.go b/actor/future_test.go
@@ -458,7 +458,8 @@ func TestCompleteWith(t *testing.T) {
 }
 
 // TestAwaitFuture verifies that AwaitFuture unpacks a resolved future into a
-// (value, nil) pair and that context cancellation before resolution is
+// (value, nil) pair, that a future completed with fn.Err is reported as a
+// (zero, err) pair, and that context cancellation before resolution is
 // reported as a (zero, ctx.Err()) pair.
 func TestAwaitFuture(t *testing.T) {
 	t.Parallel()
@@ -471,6 +472,16 @@ func TestAwaitFuture(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, "hello", val)
 
+	// Future completed with fn.Err — should surface the error as the
+	// second return value with the zero string value.
+	sentinel := fmt.Errorf("result-level error")
+	errPromise := NewPromise[string]()
+	errPromise.Complete(fn.Err[string](sentinel))
+
+	val3, err3 := AwaitFuture(context.Background(), errPromise.Future())
+	require.ErrorIs(t, err3, sentinel)
+	require.Equal(t, "", val3, "zero value expected on fn.Err result")
+
 	// Cancelled context — should return the zero value and ctx.Err().
 	unresolved := NewPromise[string]()
 	ctx, cancel := context.WithCancel(context.Background())
