gistfile1.txt

// a.m
@implementation XXX 
- (BOOL)doX:(NSError **)error {
   if([self success] == NO) {
      if(error == NULL) {
         log(bla);
      }
   }
}
@end

// test.swift

func test_doX() {
  try? doX() // Swift always passes an error to doX: - so line 6 can never be reached with a test. 
}