Jest Node.js and React

#webdev #programming #javascript #beginners

Here's a Jest cheat sheet summarizing its key features for writing effective unit tests in your Node.js and React projects:

1. Test Structure:

it function: Defines a single test case.
- describe block (optional): Groups related test cases.

describe("MyComponent", () => {
  it("should render correctly", () => {
    // Your test code here
  });
});

2. Matchers:

Basic matchers:
- toBe: Checks strict equality (===)
- toEqual: Checks deep equality (regardless of object structure)
- toBeNull
- toBeUndefined
- toBeTruthy
- toBeFalsy
Number matchers:
- toBeGreaterThan
- toBeLessThan
- toBeCloseTo (allows for a precision parameter)
String matchers:
- toContain (checks if a substring exists)
- toMatch (checks for a regular expression match)
Array/Object matchers:
- toContainEqual (checks if an array contains all elements in another array)
- toMatchObject (checks if an object contains all properties and values in another object)

3. Mocking:

jest.fn(): Creates a mock function for testing dependencies.
Mock assertions:
- toHaveBeenCalled: Checks if the function was called.
- toHaveBeenCalledWith: Checks if the function was called with specific arguments.
- toHaveReturnedWith: Checks the function's return value.

4. Snapshot Testing:

toMatchSnapshot: Takes a snapshot of a value and compares it to a previously saved snapshot.
Useful for ensuring UI components render consistently.

5. Async/Await Testing: