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Added some new tests for the function #102

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Added some new tests for the function #102

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7e1ff47
Added some new tests for the function
GeorgeSavostikov Mar 29, 2026
f5252dc
Deleted one test
GeorgeSavostikov Mar 29, 2026
d62bdd3
Returned one test
GeorgeSavostikov Mar 29, 2026
494e8f1
Changed one test
GeorgeSavostikov Mar 29, 2026
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67 changes: 65 additions & 2 deletions src/reduce.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,70 @@ describe('reduce', () => {
delete Array.prototype.reduce2;
});

it('should ', () => {});
it('should be declared', () => {
expect(Array.prototype.reduce2).toBeInstanceOf(Function);
});

it('should sum array with initial value', () => {
const array = [1, 2, 3, 4, 5, 6];
const callback = jest.fn((prev, x) => prev + x);

const result = array.reduce2(callback, 0);

expect(result).toBe(21);
expect(callback).toHaveBeenCalledTimes(6);
});

it('should sum array without initial value', () => {
const array = [1, 2, 3, 4, 5, 6];
const callback = jest.fn((prev, x) => prev + x);

const result = array.reduce2(callback);

expect(result).toBe(21);
expect(callback).toHaveBeenCalledTimes(5);
});

it('should return initial value for empty array', () => {
const array = [];

const callback = jest.fn((prev, x) => prev + x);

const result = array.reduce2(callback, 0);

expect(result).toBe(0);
expect(callback).not.toHaveBeenCalled();
});

// Add tests here
it('should return undefined for empty array without initial value', () => {
const array = [];

const callback = jest.fn((prev, x) => prev + x);

const result = () => array.reduce(callback);

expect(result).toThrow();
});
Comment on lines +49 to +57
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@mateacademy-ai-mentor mateacademy-ai-mentor Mar 29, 2026

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This test case has a few issues that need to be addressed:

  1. Incorrect Function Call: You are testing the native array.reduce() method here, not your custom array.reduce2(). The test should validate your own implementation.
  2. Inaccurate Test Description: The title states it should return undefined, but according to the reduce specification, calling it on an empty array without an initial value must throw a TypeError.
  3. Imprecise Assertion: The assertion should be more specific. Instead of .toThrow(), please check for the exact error type: .toThrow(TypeError).


it('should work with single element and initial value', () => {
const array = [1];

const callback = jest.fn((prev, x) => prev + x);

const result = array.reduce2(callback, 2);

expect(result).toBe(3);
expect(callback).toHaveBeenCalledTimes(1);
});

it('should return element if single element and no initial value', () => {
const array = [1];

const callback = jest.fn((prev, x) => prev + x);

const result = array.reduce2(callback);

expect(result).toBe(1);
expect(callback).not.toHaveBeenCalled();
});
});
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