And that's what the test expects. Both the are lowercase. Not a kata issue.

When studying the testing code, I noticed that the line test.assert_equals(to_camel_case("the_stealth_warrior"), "theStealthWarrior", "to_camel_case('the_stealth_warrior') did not return correct value") expects the result of calling the function to_camel_case("the_stealth_warrior" ) will be equal to "theStealthWarrior". However, according to the conditions of the task, the first word should be capitalized only if the original word was capitalized. In the case of "the_stealth_warrior", the first word "the" starts with a lowercase letter and must remain the same in the resulting string.