How to do it...

1. From the Content Browser, go to Add New | New C++ Class. From the menu that pops up, scroll down all the way until you see the Unreal Interface selection and select it. Afterward, click on the Next button:

2. From there, verify that the Name of the class is MyInterface and then click on the Create Class button:

3. Add the following code to the header file:

#pragma once

#include "CoreMinimal.h"
#include "UObject/Interface.h"
#include "MyInterface.generated.h"

// This class does not need to be modified.
UINTERFACE(MinimalAPI)
class UMyInterface : public UInterface
{
  GENERATED_BODY()
};

class CHAPTER_07_API IMyInterface
{
  GENERATED_BODY()

  // Add interface functions to this class. This is the class that   
  //will be inherited to implement this interface.

public:
    virtual FString GetTestName();
};

4. Implement the class with this code in the .cpp file:

#include "MyInterface.h"

// Add default functionality here for any IMyInterface functions that are not pure virtual.
FString IMyInterface::GetTestName()
{
    unimplemented();
    return FString();
}

5. Compile your project to verify that the code was written without errors.