Simulated static functions are invoked within the main function under evaluation

Question

Simulated static functions are invoked within the main function under evaluation

Looking to mock certain functions within a function I'm currently testing.

In my code, there is a class with various static private functions that are called by the main function. Specifically, I want to verify the output of MyClass.functionD (which is invoked by mainFunction, a private method). To do this, I aim to mock MyClass.functionA, MyClass.functionB, and MyClass.functionC to return default results, allowing me to focus on the outcome of MyClass.functionD in my test.

export default class MyClass {

   static mainFunction(paramA: string, paramB: number): boolean {

        if (MyClass.functionA(paramA, paramB)) {
            return false;
        }

        if (!MyClass.functionB(paramA, paramB)) {
            return false;
        }

        if (MyClass.functionC(paramA, paramB)) {
            return false;
        }

        // Need to concentrate on the result of this private function for testing
        if (MyClass.functionD(paramA)) {
            return false;
        }

        return true;
   }

}

I've experimented with jest spyOn and default mock functions but feel stuck due to my limited experience with TypeScript/Javascript. Any pointers or references on how to proceed would be greatly appreciated! Thanks in advance.

javascript typescript unit-testing jestjs mocking

Answer 1

Answer №1

The TypeScript public and private keywords are used for code validation purposes only and do not affect the JavaScript output. You can still access these private methods using bracket notation like MyClass['functionA'] to ignore TypeScript's type checking. This allows you to mock these private methods using jest.spyOn.

For your testing strategy, consider the following:

MyClass.ts:

export default class MyClass {
  static mainFunction(paramA: string, paramB: number): boolean {
    if (MyClass.functionA(paramA, paramB)) {
      return false;
    }

    if (!MyClass.functionB(paramA, paramB)) {
      return false;
    }

    if (MyClass.functionC(paramA, paramB)) {
      return false;
    }

    if (MyClass.functionD(paramA)) {
      return false;
    }

    return true;
  }

  private static functionA(a, b) {
    return true;
  }

  private static functionB(a, b) {
    return false;
  }

  private static functionC(a, b) {
    return true;
  }
  
  private static functionD(a) {
    return false;
  }
}

MyClass.test.ts:

import MyClass from './MyClass';

describe('65376946', () => {
  afterEach(() => {
    jest.restoreAllMocks();
  });
  it('should pass', () => {
    const functionASpy = jest.spyOn(MyClass as any, 'functionA').mockReturnValueOnce(false);
    const functionBSpy = jest.spyOn(MyClass as any, 'functionB').mockReturnValueOnce(true);
    const functionCSpy = jest.spyOn(MyClass as any, 'functionC').mockReturnValueOnce(false);
    const functionDSpy = jest.spyOn(MyClass as any, 'functionD').mockReturnValueOnce(true);

    const actual = MyClass.mainFunction('a', 1);
    expect(actual).toBeFalsy();
    expect(functionASpy).toBeCalledWith('a', 1);
    expect(functionBSpy).toBeCalledWith('a', 1);
    expect(functionCSpy).toBeCalledWith('a', 1);
    expect(functionDSpy).toBeCalledWith('a');
  });
});

Unit test results:

PASS  examples/65376946/MyClass.test.ts
  65376946
    ✓ should pass (3 ms)

------------|---------|----------|---------|---------|-------------------
File        | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
------------|---------|----------|---------|---------|-------------------
All files   |   42.86 |       50 |      20 |   42.86 |                   
 MyClass.ts |   42.86 |       50 |      20 |   42.86 | 4,8,12,19-34      
------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        4.168 s

Answer 2

The TypeScript public and private keywords are used for code validation purposes only and do not affect the JavaScript output. You can still access these private methods using bracket notation like MyClass['functionA'] to ignore TypeScript's type checking. This allows you to mock these private methods using jest.spyOn.

For your testing strategy, consider the following:

MyClass.ts:

export default class MyClass {
  static mainFunction(paramA: string, paramB: number): boolean {
    if (MyClass.functionA(paramA, paramB)) {
      return false;
    }

    if (!MyClass.functionB(paramA, paramB)) {
      return false;
    }

    if (MyClass.functionC(paramA, paramB)) {
      return false;
    }

    if (MyClass.functionD(paramA)) {
      return false;
    }

    return true;
  }

  private static functionA(a, b) {
    return true;
  }

  private static functionB(a, b) {
    return false;
  }

  private static functionC(a, b) {
    return true;
  }
  
  private static functionD(a) {
    return false;
  }
}

MyClass.test.ts:

import MyClass from './MyClass';

describe('65376946', () => {
  afterEach(() => {
    jest.restoreAllMocks();
  });
  it('should pass', () => {
    const functionASpy = jest.spyOn(MyClass as any, 'functionA').mockReturnValueOnce(false);
    const functionBSpy = jest.spyOn(MyClass as any, 'functionB').mockReturnValueOnce(true);
    const functionCSpy = jest.spyOn(MyClass as any, 'functionC').mockReturnValueOnce(false);
    const functionDSpy = jest.spyOn(MyClass as any, 'functionD').mockReturnValueOnce(true);

    const actual = MyClass.mainFunction('a', 1);
    expect(actual).toBeFalsy();
    expect(functionASpy).toBeCalledWith('a', 1);
    expect(functionBSpy).toBeCalledWith('a', 1);
    expect(functionCSpy).toBeCalledWith('a', 1);
    expect(functionDSpy).toBeCalledWith('a');
  });
});

Unit test results:

PASS  examples/65376946/MyClass.test.ts
  65376946
    ✓ should pass (3 ms)

------------|---------|----------|---------|---------|-------------------
File        | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
------------|---------|----------|---------|---------|-------------------
All files   |   42.86 |       50 |      20 |   42.86 |                   
 MyClass.ts |   42.86 |       50 |      20 |   42.86 | 4,8,12,19-34      
------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        4.168 s

Simulated static functions are invoked within the main function under evaluation

Answer №1

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