test("declares messageFunc and logs correct message", () => {
  expect(typeof messageFunc).toBe("function");

  const logSpy = jest.spyOn(console, "log").mockImplementation(() => {});

  messageFunc();

  expect(logSpy).toHaveBeenCalledWith("This is a message from the function");

  logSpy.mockRestore();
});

test("uses console.log inside the function", () => {
  const code = messageFunc.toString();
  expect(code.includes("console.log")).toBe(true);
});

user_code.test.js

Dive into the world of the most popular language for front-end development – JavaScript. JavaScript is a language built into almost every browser and can be used for a wide variety of tasks. Learn the basic functionality and prepare yourself for the challenges and more advanced programming techniques.

An introduction to JavaScript, covering the basic syntax of the language along with key terms and concepts that form the foundation for learning advanced features. The section includes hands-on tasks designed to help practice these concepts and make the content easy to remember without effort.

Learn how to store data and retrieve it later using variables. Additionally, explore basic data types and understand how they interact with each other.

Learn how to write expressions that evaluate to "true" or "false" based on conditions, such as "Is X equal to Y?". This will be followed by an exploration of conditional statements that allow the conditional execution of specific lines of code.

A powerful programming feature called a function allows the execution of a block of code multiple times with minimal repetition. The section introduces core concepts and syntax for defining and using functions effectively.


The concept of Arrays is introduced as a way to organize and manage collections of data. The material covers how arrays structure data and enable efficient operations on multiple values.


Loops are a fundamental feature in programming used to reduce redundancy and handle repetitive tasks efficiently. The content covers the three main types of loops in JavaScript, their syntax, use cases, and how they can be combined with arrays to streamline operations and improve performance.

Challenge: Simple Function

Solution