pub module function_test;

fn void greet() {
    let mut x = 1;
    x++;
}

pub fn void test_basic_function() {
    greet();
}

fn i32 add(a i32, b i32) {
    a + b
}

pub fn void test_fn_params() {
    assert_eq!(add(2, 3), 5);
}

pub fn i32 test_fn_return() {
    42
}

pub fn i32 test_fn_early_return() {
    return 100;
    0
}

pub fn i32 test_fn_mut_param(mut x i32) {
    x = x + 10;
    x
}

pub fn void test_method_call() {
    let s = "hello";
    assert_eq!(s.len(), 5);
    assert_eq!(s.to_uppercase(), "HELLO");
}

fn i32 triple(x i32) {
    add(x, add(x, x))
}

pub fn void test_nested_fn_calls() {
    assert_eq!(triple(5), 15);
}

fn i32 factorial(n i32) {
    if n <= 1 { 1 }
    else { n * factorial(n - 1) }
}

pub fn void test_recursive_fn() {
    assert_eq!(factorial(5), 120);
}

pub fn void run_tests() {
    test_basic_function();
    test_fn_params();
    assert_eq!(test_fn_return(), 42);
    assert_eq!(test_fn_early_return(), 100);
    assert_eq!(test_fn_mut_param(5), 15);
    test_method_call();
    test_nested_fn_calls();
    test_recursive_fn();
}