Add some tests for NotebookTab (#5070)

* EmptyApplication: Add asserts to rest of getters (except for getSeventvAPI)

* Theme: make getTheme call getIApp()->getThemes() instead

this allows it to be used in tests
realistically this should be deprecated & users of it should just call
getIApp()->getThemes() directly

* Use getIApp() instead of getApp() in a few places

src/widgets/helper/NotebookTab.hpp

@@ -53,6 +53,8 @@ public:
     bool isLive() const;
 
     void setHighlightState(HighlightState style);
+    HighlightState highlightState() const;
+
     void setHighlightsEnabled(const bool &newVal);
     bool hasHighlightsEnabled() const;
 
@@ -84,6 +86,10 @@ protected:
     void mouseMoveEvent(QMouseEvent *event) override;
     void wheelEvent(QWheelEvent *event) override;
 
+    /// This exists as an alias to its base classes update, and is virtual
+    /// to allow for mocking
+    virtual void update();
+
 private:
     void showRenameDialog();