gistfile1.m

@interface AClassThatUsesNSWorkspace : NSObject
{
    NSWorkspace * _workspace;
}

// Production code uses this
- (id)init;

// Useful for testing (to inject a mock NSWorkspace)
- (id)initWithWorkspace:(NSWorkspace *)workspace;

- (void)openFile;

@end

@implementation AClassThatUsesNSWorkspace

- (id)init
{
    return [self initWithWorkspace:[NSWorkspace sharedWorkspace]];
}

- (id)initWithWorkspace:(NSWorkspace *)workspace
{
    self = [super init];
    if (self == nil)
        return nil;
    
    _workspace = [workspace retain];
    
    return self;
}

- (void)dealloc
{
    [_workspace release];
    [super dealloc];
}

- (void)openFile
{
    [_workspace openFile:@"file" withApplication:@"app" andDeactivate:YES];
}

@end

@interface AClassThatUsesNSWorkspaceTest : SenTestCase
@end

@implementation AClassThatUsesNSWorkspaceTest

- (void)testOpenFile
{
    id mockWorkspace = [OCMockObject mockForClass:[NSWorkspace class]];
    AClassThatUsesNSWorkspace * sut = [[[AClassThatUsesNSWorkspace alloc] initWithWorkspace:mockWorkspace] autorelease];
    
    [[mockWorkspace expect] openFile:@"file" withApplication:@"app" andDeactivate:YES];
    [sut openFile];
    
    [mockWorkspace verify];
}

@end