Testing the branch count of optional chaining in Typescript

Question

Testing the branch count of optional chaining in Typescript

I am struggling to grasp the concept of branch coverage, especially when it involves optional chaining in TypeScript.

Below is my code snippet:

type testingType = {
   b?: { a?: number };
};
 
export function example(input: testingType) {
   return input.b?.a;
}

And here is the test I wrote, although it's just for passing purposes to generate the report:

test('test', () => {
   example({});
   expect(1).toBe(1);
});

The screenshot below shows the coverage report with 3 out of 4 branches covered:

I am puzzled as to why there are a total of 4 branches. Shouldn't it be only 2 branches?

b defined
b undefined.

typescript jestjs babeljs ts-jest test-coverage

Answer 1

Answer №1

There are 3 different scenarios to consider:

{b?: { a?: number }}

The possible outcomes are as follows:

If an empty object (b is not defined): return input
If b is defined but a is not: return input.b (which will result in { b: {} })
If both b and a are defined: return input.b.a, resulting in { b: { a: SOME_NUMBER} }

Edit:

Here are the test cases that I have set up:

describe('Test suite', () => {
  test('Empty object', () => {
    example({});
    expect(1).toBe(1);
  });

  test('Only with b', () => {
    example({ b: {} });
    expect(1).toBe(1);
  });

  test('All keys provided', () => {
    example({ b: { a: 5 } });
    expect(1).toBe(1);
  });
});

Answer 2

There are 3 different scenarios to consider:

{b?: { a?: number }}

The possible outcomes are as follows:

If an empty object (b is not defined): return input
If b is defined but a is not: return input.b (which will result in { b: {} })
If both b and a are defined: return input.b.a, resulting in { b: { a: SOME_NUMBER} }

Edit:

Here are the test cases that I have set up:

describe('Test suite', () => {
  test('Empty object', () => {
    example({});
    expect(1).toBe(1);
  });

  test('Only with b', () => {
    example({ b: {} });
    expect(1).toBe(1);
  });

  test('All keys provided', () => {
    example({ b: { a: 5 } });
    expect(1).toBe(1);
  });
});

Testing the branch count of optional chaining in Typescript

Answer №1

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