Unit Testing Question:

Unit Testing Question:

I have a class which implements an interface, and I want to unit test it. I am testing the class, so my test code references the class.

However, in my class, it passes itself as an interface reference to another interface, and when this happens, my test class cannot be Freed and breaks.

The code below shows my problem (I use DUNITX).

Main has a field ISub, which knows about IMain.

When IMain is created, it passes itself as a reference to ISub (TMain -> IMain cast)

when I call FMain.Free; it breaks with an "invalid pointer operation" as it has been used as an interface.

test code:

type
Isub = interface end;
IMain = interface end;

TSub = class( TInterfacedObject, Isub )
FMain: IMain;
constructor Create( const AOwner: IMain);
end;

TMain = class( TInterfacedObject, IMain )
FSub: Isub;
constructor Create;
destructor Destroy; override;
end;

[TestFixture]
TUT_TEST = class
private
FMain : TMain;
public
[Setup] procedure Setup;
[Teardown] procedure Teardown;

[Test] procedure A;
end;

implementation

constructor TSub.Create(const AOwner: IMain);
begin
inherited Create;

FMain := AOwner;
end;

constructor TMain.Create;
begin
inherited;

FSub := TSub.Create( Self );
end;
destructor TMain.Destroy;
begin
inherited; // <-- never reach this line
end;

procedure TUT_TEST.Setup;
begin
FMain := TMain.Create;
end;
procedure TUT_TEST.Teardown;
begin
if Assigned( FMain ) then
FMain.Free; // <-- fail as this has been referenced as an interface
FMain := nil;
end;

procedure TUT_TEST.A;
begin
Assert.IsNotNull( FMain );
end;


So, I have the following questions:
How do you test the class when this happens?
Would you just test the interface instead, avoiding this problem?
Do I ignore the Free in my Teardown and just let it be handled as an interface?

In my code, ISub must know about its owner in order to call it. This COULD be done with events, but it is not a problem in production as everything is interfaces, only by adhering to the rule of testing the class rather than the interface am I having this issue.

Any help would be great!