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

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

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

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

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