#[cfg(test)]
mod tests {
    use crate::negation_normal_form::negation_normal_form;

    #[test]
    fn double_neg_simple() {
        assert_eq!(negation_normal_form("A!!"), "A");
        assert_eq!(negation_normal_form("B!!!!"), "B");
        assert_eq!(negation_normal_form("C!!!"), "C!");
        assert_eq!(negation_normal_form("D!!!!!!!!!!!!!!!!"), "D");
        assert_eq!(negation_normal_form("E!!!!!!!!!!!!!!!"), "E!");
    }

    #[test]
    fn double_neg() {
        assert_eq!(negation_normal_form("A!!Z&"), "AZ&");
        assert_eq!(negation_normal_form("B!!Z!!&"), "BZ&");
        assert_eq!(negation_normal_form("C!!Z!&"), "CZ!&");
        assert_eq!(negation_normal_form("D!!Z&!!!!"), "DZ&");
        assert_eq!(negation_normal_form("E!!Z!!!!&!!"), "EZ&");
        assert_eq!(negation_normal_form("F!!Z!&!!!!!!!!"), "FZ!&");
    }

    #[test]
    fn neg_and() {
        assert_eq!(negation_normal_form("AZ&!"), "A!Z!|");
        assert_eq!(negation_normal_form("BZ&!BZ&!&"), "B!Z!|B!Z!|&");
        assert_eq!(negation_normal_form("CZ&!CZ&!&!"), "CZ&CZ&|");
    }

    #[test]
    fn neg_or() {
        assert_eq!(negation_normal_form("AZ|!"), "A!Z!&");
        assert_eq!(negation_normal_form("BZ|!BZ|!|"), "B!Z!&B!Z!&|");
        assert_eq!(negation_normal_form("CZ|!CZ|!|!"), "CZ|CZ|&");
    }

    #[test]
    fn material_condition() {
        assert_eq!(negation_normal_form("AZ>"), "A!Z|");
        assert_eq!(negation_normal_form("BZ>!"), "BZ!&");
    }

    #[test]
    fn exclusive_disjunction() {
        assert_eq!(negation_normal_form("AZ^"), "AZ|A!Z!|&");
        assert_eq!(negation_normal_form("BZ^!"), "B!Z!&BZ&|");
    }

    #[test]
    fn logical_equivalence() {
        assert_eq!(negation_normal_form("AZ="), "A!Z|Z!A|&");
        assert_eq!(negation_normal_form("BZ=!"), "BZ!&ZB!&|");
    }

    #[test]
    fn subject_tests() {
        assert_eq!(negation_normal_form("AB&!"), "A!B!|");
        assert_eq!(negation_normal_form("AB|!"), "A!B!&");
        assert_eq!(negation_normal_form("AB>"), "A!B|");
        assert_eq!(negation_normal_form("AB|C&!"), "A!B!&C!|");
    }

    #[test]
    fn complex_tests() {
        assert_eq!(negation_normal_form("AB=CD^|!AD!^!&!"), "A!B|B!A|&CD|C!D!|&|AD!|A!D|&|");
    }
}