Present help failures through the common diagnostic path

execute_external_test.go

@@ -413,3 +413,27 @@ func (shortWriter) Write(data []byte) (int, error) {
 	}
 	return len(data) - 1, nil
 }
+
+func TestHelpEntryFormsPresentReportAndDiagnosticFailures(t *testing.T) {
+	group, err := commandkit.Group("notes", "Notes metadata.")
+	if err != nil {
+		t.Fatal(err)
+	}
+	app, err := commandkit.New(commandkit.Identity{Name: "example"}, group)
+	if err != nil {
+		t.Fatal(err)
+	}
+	reportErr := errors.New("report failed")
+	diagnosticErr := errors.New("diagnostic failed")
+	for _, args := range [][]string{nil, {"notes"}, {"--help"}, {"-h"}, {"notes", "--help"}, {"help"}, {"help", "notes"}} {
+		var diagnostics bytes.Buffer
+		result := app.Execute(context.Background(), args, commandkit.Streams{Out: failingWriter{reportErr}, Err: &diagnostics})
+		if result.Kind != commandkit.OutcomeOperational || !result.ReportIncomplete || !errors.Is(result.Cause, reportErr) || !errors.Is(result.DeliveryError, reportErr) || result.DiagnosticDelivery != commandkit.DeliveryComplete || strings.Count(diagnostics.String(), reportErr.Error()) != 1 {
+			t.Fatalf("%v: result=%#v diagnostics=%q", args, result, diagnostics.String())
+		}
+		result = app.Execute(context.Background(), args, commandkit.Streams{Out: failingWriter{reportErr}, Err: failingWriter{diagnosticErr}})
+		if result.DiagnosticDelivery != commandkit.DeliveryIncomplete || !errors.Is(result.Cause, reportErr) || !errors.Is(result.DeliveryError, reportErr) || !errors.Is(result.DeliveryError, diagnosticErr) {
+			t.Fatalf("%v: result=%#v", args, result)
+		}
+	}
+}