Counting words with a given prefix

#[test]
fn t1() {
    let start = std::time::Instant::now();
    let val = Solution::prefix_count(vec!["pay".to_string(), "attention".to_string(), "practice".to_string(), "attend".to_string()], "at".to_string());
    let expected = 2;
    log_result!(val == expected, "t1", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t2() {
    let start = std::time::Instant::now();
    let val = Solution::prefix_count(vec!["leetcode".to_string(), "win".to_string(), "loops".to_string(), "success".to_string()], "code".to_string());
    let expected = 0;
    log_result!(val == expected, "t2", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t3() {
    let start = std::time::Instant::now();
    let val = Solution::prefix_count(vec!["abc".to_string()], "abc".to_string());
    let expected = 1;
    log_result!(val == expected, "t3", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t4() {
    let start = std::time::Instant::now();
    let val = Solution::prefix_count(vec!["a".to_string(), "b".to_string(), "c".to_string()], "".to_string());
    let expected = 3;
    log_result!(val == expected, "t4", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t5() {
    let start = std::time::Instant::now();
    let val = Solution::prefix_count(vec!["ab".to_string(), "abc".to_string()], "abcd".to_string());
    let expected = 0;
    log_result!(val == expected, "t5", start, &expected, &val);
    assert_eq!(val, expected);
}