Label printing unit test (#3047)

* Adds a very simple sample plugin for label printing

* Test mixin install status and API query

* Better error reporting for label printing API

* pep fixes

* fix assertation

* remove broken assertation

* igonre for coverage

* test the base process of printing

* refactor tests

* clean up basic test

* refactor url

* fix url creation

* test printing multiples

* test all printing endpoints

* test all list options - move api tests

* test for invalid filters

* refactor

* test with no part

* these should not happen
checks are in place upstream

* fix assertation

* do not cover continue parts

* test for wrong implementation

* ignore DB not ready

* remove covage from default parts

* fix url generation

* test debug mode

* fix url assertation

* check that nothing was rendered

Co-authored-by: Oliver Walters <oliver.henry.walters@gmail.com>

InvenTree/plugin/base/label/label.py

@@ -26,13 +26,13 @@ def print_label(plugin_slug, label_image, label_instance=None, user=None):
 
     plugin = registry.plugins.get(plugin_slug, None)
 
-    if plugin is None:
+    if plugin is None:  # pragma: no cover
         logger.error(f"Could not find matching plugin for '{plugin_slug}'")
         return
 
     try:
         plugin.print_label(label_image, width=label_instance.width, height=label_instance.height)
-    except Exception as e:
+    except Exception as e:  # pragma: no cover
         # Plugin threw an error - notify the user who attempted to print
 
         ctx = {