Check if all as appears before all bs

#[test]
fn t1() {
    let start = std::time::Instant::now();
    let val = Solution::check_string("aaabbb".to_string());
    let expected = true;
    log_result!(val == expected, "t1", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t2() {
    let start = std::time::Instant::now();
    let val = Solution::check_string("abab".to_string());
    let expected = false;
    log_result!(val == expected, "t2", start, &expected, &val);
    assert_eq!(val, expected);
}

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

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

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