Camel Case Breaker solution https://dev.to/thepracticaldev/daily-challenge-188-break-camelcase-3ppf

ccbreaker.rs

pub fn ccbreaker (value: &str) -> String {
    value.chars()
        .into_iter()
        .map(|c| if c.is_uppercase() { format!(" {}", c.to_lowercase()) } else { c.to_string() })
        .collect::<String>()
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn example_1() {
        assert_eq!(ccbreaker("camelCasing"), "camel casing".to_string());
    }
    #[test]
    fn example_2() {
        assert_eq!(ccbreaker("garbageTruck"), "garbage truck".to_string());
    }
    #[test]
    fn test_1() {
        assert_eq!(ccbreaker("policeSiren"), "police siren".to_string());
    }
    #[test]
    fn test_2() {
        assert_eq!(ccbreaker("camelCasingTest"), "camel casing test".to_string());
    }
}