I've created a tab via blender python interface but it doesn't appear when script executed

Question

I just started out learning script making in blender and created a code that suppose to create new tab in object preferences tab when executed. But it does not happen. But according to console messages the script is successfully executed. I tried out Python template for UI panel that was directly in Blender Text editor space but it does not work either. What am I missing?

Here's the code itself:

    import bpy

class Testpanel (bpy.types.Panel):
    bl_label = "Testpanel"
    bl_idname = "PT_testpanel"
    bl_space_type = 'ViEW_3D'
    bl_region_type = 'UI'
    bl_category = "NewTab"
    
    
    def draw (self, context):
        layout = self.layout
        
        row = layout.row ()
        row.label (text= "Sample text")
        
        
  
def register ():
    bpy.utils.register_class (Testpanel)
    
def unregister ():
    bpy.utils.unregister_class (Testpanel)
    
    if __name__ == '__main__':
        register ()

Also the code I tried running that was from Blender python templates menu. Which also does not seem to work

import bpy

class Testpanel (bpy.types.Panel):
    bl_label = "Testpanel"
    bl_idname = "PT_testpanel"
    bl_space_type = 'ViEW_3D'
    bl_region_type = 'UI'
    bl_category = "NewTab"
    
    
    def draw (self, context):
        layout = self.layout
        
        row = layout.row ()
        row.label (text= "Sample text")
        
        
        
        
        
        
        
def register ():
    bpy.utils.register_class (Testpanel)
    
def unregister ():
    bpy.utils.unregister_class (Testpanel)
    
    if __name__ == '__main__':
        register ()