Add comment to test

tests/test_gui/test_gui_theme.py

@@ -431,11 +431,13 @@ def testGuiTheme_LoadIcons():
     assert qIcon.isNull() is False
 
     # Load it as a pixmap with a size
+    # If this part of the test fails, you may need to set the
+    # environment variable: QT_SCALE_FACTOR=1
     qPix = iconCache.getPixmap("add", (50, 50))
     assert isinstance(qPix, QPixmap)
     assert qPix.isNull() is False
-    assert qPix.width() == 50
-    assert qPix.height() == 50
+    assert qPix.width() == 50, "If this fails, make sure QT_SCALE_FACTOR=1"
+    assert qPix.height() == 50, "If this fails, make sure QT_SCALE_FACTOR=1"
 
     # Load app icon
     qIcon = iconCache.getIcon("novelwriter")