import Control.Monad

import qualified Data.Map as Map

readLines :: Int -> IO [String]

readLines n

| n == 0 = return []

| otherwise = do

s <- getLine

otherLines <- readLines (n - 1)

return $ s : otherLines

functionChecker :: (Bool, Map.Map Int Int) -> [Int] -> (Bool, Map.Map Int Int)

functionChecker (fails, m) [k, v] =

(fails || (Map.member k m && (Map.!) m k /= v), Map.insert k v m)

main = do

t <- readLn :: IO Int

forM_ [1 .. t] $ \ca -> do

n <- readLn :: IO Int

funcText <- readLines n

let mappings = map (map (read :: String -> Int) . words) funcText

putStrLn $ if fst $ foldl functionChecker (False, Map.empty) mappings

then "NO"

else "YES"