Number of pairs of strings with concatenation equal to target

#[test]
fn test_basic1() {
    let start = std::time::Instant::now();
    let val = Solution::num_of_pairs(vec!["777".to_string(), "7".to_string(), "77".to_string(), "77".to_string()], "7777".to_string());
    let expected = 4;
    log_result!(val == expected, "test_basic1", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_basic2() {
    let start = std::time::Instant::now();
    let val = Solution::num_of_pairs(vec!["123".to_string(), "4".to_string(), "12".to_string(), "34".to_string()], "1234".to_string());
    let expected = 2;
    log_result!(val == expected, "test_basic2", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_basic3() {
    let start = std::time::Instant::now();
    let val = Solution::num_of_pairs(vec!["1".to_string(), "1".to_string(), "1".to_string()], "11".to_string());
    let expected = 6;
    log_result!(val == expected, "test_basic3", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_no_pairs() {
    let start = std::time::Instant::now();
    let val = Solution::num_of_pairs(vec!["1".to_string(), "2".to_string()], "13".to_string());
    let expected = 0;
    log_result!(val == expected, "test_no_pairs", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_single_pair() {
    let start = std::time::Instant::now();
    let val = Solution::num_of_pairs(vec!["ab".to_string(), "c".to_string(), "a".to_string(), "bc".to_string()], "abc".to_string());
    let expected = 2;
    log_result!(val == expected, "test_single_pair", start, &expected, &val);
    assert_eq!(val, expected);
}