Adding to Menu Entries in UE4 editor

customtestplugin.build.cs

// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.

using UnrealBuildTool;

public class CustomTestPlugin : ModuleRules
{
	public CustomTestPlugin(ReadOnlyTargetRules Target) : base(Target)
	{
		PCHUsage = ModuleRules.PCHUsageMode.UseExplicitOrSharedPCHs;
		
		PublicIncludePaths.AddRange(
			new string[] {
                "CustomTestPlugin/Public"
				// ... add public include paths required here ...
			}
			);
				
		
		PrivateIncludePaths.AddRange(
			new string[] {
                "CustomTestPlugin/Private"
				// ... add other private include paths required here ...
			}
			);
			
		
		PublicDependencyModuleNames.AddRange(
			new string[]
			{
				"Core",
                "TestCPP"
				// ... add other public dependencies that you statically link with here ...
			}
			);
			
		
		PrivateDependencyModuleNames.AddRange(
			new string[]
			{
				"CoreUObject",
				"Engine",
				"Slate",
				"SlateCore",
                "LevelEditor",
                "EditorStyle",
				// ... add private dependencies that you statically link with here ...	
			}
			);
		
		
		DynamicallyLoadedModuleNames.AddRange(
			new string[]
			{
				// ... add any modules that your module loads dynamically here ...
			}
			);
	}
}

customtestplugin.cpp

// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.

#include "CustomTestPlugin.h"
#include "LevelEditor.h"
#include "Misc/Attribute.h"

#define LOCTEXT_NAMESPACE "FCustomTestPluginModule"

void FCustomTestPluginModule::StartupModule()
{
	UE_LOG(LogTemp, Warning, TEXT("Starting Module...."));
	
	// Create the Extender that will add content to the menu
	FLevelEditorModule& LevelEditorModule = FModuleManager::LoadModuleChecked<FLevelEditorModule>("LevelEditor");
	TSharedPtr<FExtender> MenuExtender = MakeShareable(new FExtender());
	//MenuExtender->AddToolBarExtension("Content", EExtensionHook::Before,);
	MenuExtender->AddMenuExtension(
		"LevelEditor",
		EExtensionHook::After,
		NULL,
		FMenuExtensionDelegate::CreateRaw(this, &FCustomTestPluginModule::AddMenuEntry)
	);
	LevelEditorModule.GetMenuExtensibilityManager()->AddExtender(MenuExtender);
	// This code will execute after your module is loaded into memory; the exact timing is specified in the .uplugin file per-module
}

void FCustomTestPluginModule::ShutdownModule()
{
	UE_LOG(LogTemp, Warning, TEXT("Stopping Module...."));	
	// This function may be called during shutdown to clean up your module.  For modules that support dynamic reloading,
	// we call this function before unloading the module.
}

void FCustomTestPluginModule::AddMenuEntry(FMenuBuilder & MenuBuilder)
{
	// Create Section
	MenuBuilder.BeginSection("CustomMenu", TAttribute<FText>(FText::FromString("Category/Section Name")));
	{
		MenuBuilder.AddSubMenu(FText::FromString("My Submenu"),
			FText::FromString("My submenu tooltip"),
			FNewMenuDelegate::CreateRaw(this, &FCustomTestPluginModule::FillSubmenu));
	}
	MenuBuilder.EndSection();
}

void FCustomTestPluginModule::FillSubmenu(FMenuBuilder& MenuBuilder)
{
	// Create the Submenu Entries
	MenuBuilder.AddMenuEntry(
		FText::FromString("Menu Entry 1"),
		FText::FromString("Menu Entry 1 Tooltip"),
		FSlateIcon(),
		FUIAction(FExecuteAction::CreateRaw(this, &FCustomTestPluginModule::MenuCallback1))
	);

}


void FCustomTestPluginModule::MenuCallback1() {
	UE_LOG(LogTemp, Warning, TEXT("Action 1!"));
}


#undef LOCTEXT_NAMESPACE
	
IMPLEMENT_MODULE(FCustomTestPluginModule, CustomTestPlugin)

customtestplugin.h

// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.

#pragma once

#include "CoreMinimal.h"
#include "Engine.h"
#include "Modules/ModuleManager.h"

class FToolBarBuilder;


class FCustomTestPluginModule : public IModuleInterface
{
public:

	/** IModuleInterface implementation */
	virtual void StartupModule() override;
	virtual void ShutdownModule() override;
private:
	void AddMenuEntry(class FMenuBuilder& MenuBuilder);
	void FillSubmenu(FMenuBuilder& MenuBuilder);
	void MenuCallback1();
};