assert_eq(str_length(""), 0)
assert_eq(str_length("foo"), 3)

assert_eq(str_slice(0, 5, "hello world"), "hello")
assert_eq(str_slice(6, 11, "hello world"), "world")
assert_eq(str_slice(0, 0, "hello world"), "")
assert_eq(str_slice(0, 100, "hello world"), "")

assert_eq(chr(65), "A")
assert_eq(chr(97), "a")
assert_eq(chr(0x2764), "❤")

assert_eq(ord("A"), 65)
assert_eq(ord("a"), 97)
assert_eq(ord("❤"), 0x2764)

assert_eq(str_append("foo", "bar"), "foobar")
assert_eq(str_prepend("bar", "foo"), "foobar")

assert(str_contains("hello", "hello world"))
assert(str_contains("world", "hello world"))
assert_eq(str_contains("HELLO", "hello world"), false)

assert_eq(str_replace("hello", "HEY", "hello world"), "HEY world")
assert_eq(str_replace("x", "yY", "xxx"), "yYyYyY")
assert_eq(str_replace(" ", "   ", "a b"), "a   b")

assert_eq(str_repeat(3, "xy"), "xyxyxy")