func testPhoneNumbers(_ numbers: [String]) -> Bool {
    var tmp = numbers
    while !tmp.isEmpty {
        let numberToTest = tmp.removeFirst()
        if !tmp.allSatisfy({ !$0.hasPrefix(numberToTest) }) {
            return false
        }
    }
    return true
}

let testCount = Int(readLine()!)!

for _ in 1...testCount {
    let phoneNumberCount = Int(readLine()!)!
    var phoneNumbers = [String]()
    for _ in 1...phoneNumberCount {
        phoneNumbers.append(readLine()!)
    }
    phoneNumbers.sort()
    print(testPhoneNumbers(phoneNumbers) ? "YES" : "NO")
}