CodeSignal provides an IDE within the assessment in which to code your solutions. It has several formatting options such as autocomplete, 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.
Click the Gear icon in the upper right hand corner of the IDE (next to the "Reset" button) to choose various formatting options such as editor mode, IDE theme, tab size, font size, etc:
Here is how the IDE appears within a task: