CodeSignal provides an IDE within the assessment in which to code your solutions. It has some autocomplete capabilities and shows a set of sample test cases that your code will be checked against. Clicking SUBMIT will run your code against our full suite of test cases, including some hidden test cases, and your score will be based on how many total test cases (sample and hidden) you are able to pass.
You may also change some formatting options such as editor mode, IDE theme, tab size, font size, etc:
Here is how the IDE appears within a task: