Test: [skip ci] limit the text in the error dialog to 1000 chars as otherwise it can become larger than the available vertical space of the desktop

src/Mod/Test/Gui/UnitTestImp.cpp

@@ -139,6 +139,9 @@ void UnitTestDialog::on_treeViewFailure_itemDoubleClicked(QTreeWidgetItem * item
         lines.erase(lines.begin()+20, lines.end());
         text = lines.join(QLatin1String("\n"));
     }
+    if (text.size() > 1000) {
+        text = text.left(1000);
+    }
 
     msgBox.setText(text);
     msgBox.exec();