简单NSImage图形未按预期工作

这没有任何作用:

NSImage* testImage = [[NSImage alloc] initWithSize:NSMakeSize(2.0,2.0)];

[testImage lockFocus];
[[NSImage imageNamed:@"testImage"] drawAtPoint:NSMakePoint(1.0,1.0) fromRect:NSZeroRect operation:NSCompositeCopy fraction:1.0];
[testImage unlockFocus];

[levelView setImage:testImage];

[levelView setImage:[NSImage imageNamed:@"testImage"]];

在我看来,如果后者产生了明显的结果,那么前者也应该如此。我想我在什么地方犯了个愚蠢的错误?