Percentage of letter in string

#[test]
fn t1() {
    let start = std::time::Instant::now();
    let val = Solution::percentage_letter("foobar".to_string(), 'o');
    let expected = 33;
    log_result!(val == expected, "t1", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t2() {
    let start = std::time::Instant::now();
    let val = Solution::percentage_letter("jjjj".to_string(), 'k');
    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::percentage_letter("aaaa".to_string(), 'a');
    let expected = 100;
    log_result!(val == expected, "t3", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t4() {
    let start = std::time::Instant::now();
    let val = Solution::percentage_letter("a".to_string(), 'a');
    let expected = 100;
    log_result!(val == expected, "t4", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t5() {
    let start = std::time::Instant::now();
    let val = Solution::percentage_letter("abcdef".to_string(), 'a');
    let expected = 16;
    log_result!(val == expected, "t5", start, &expected, &val);
    assert_eq!(val, expected);
}