Check if a word occurs as a prefix of any word in a sentence

#[test]
fn t1() {
    let start = std::time::Instant::now();
    let val = Solution::is_prefix_of_word("i love eating burger".to_string(), "burg".to_string());
    let expected = 4;
    log_result!(val == expected, "t1", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t2() {
    let start = std::time::Instant::now();
    let val = Solution::is_prefix_of_word("this problem is an easy problem".to_string(), "pro".to_string());
    let expected = 2;
    log_result!(val == expected, "t2", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t3() {
    let start = std::time::Instant::now();
    let val = Solution::is_prefix_of_word("i am tired".to_string(), "you".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::is_prefix_of_word("hello world".to_string(), "world".to_string());
    let expected = 2;
    log_result!(val == expected, "t4", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t5() {
    let start = std::time::Instant::now();
    let val = Solution::is_prefix_of_word("a".to_string(), "a".to_string());
    let expected = 1;
    log_result!(val == expected, "t5", start, &expected, &val);
    assert_eq!(val, expected);
}