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

pub fn test_basic_function() {
    greet();
}

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

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

pub fn test_fn_return() i32 {
    42
}

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

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

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

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

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

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

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

pub fn 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();
}