How to jest.mock "git-simple" branchLocal function?

Question

I use the simple-git package. I have the following function:

import simpleGit from 'simple-git';

/**
 * The function returns the ticket Id, is presents, in the branch name
 * @returns ticket Id
 */
export const getTicketIdFromBranchName = async (ticketRegex: RegExp) => {
    const git = simpleGit();

    try {
        const localBranches = await git.branchLocal();
        const currentBranch = localBranches.current;
        const currentBranchTicketMatches = currentBranch.match(ticketRegex);

        if (currentBranchTicketMatches) {
            return currentBranchTicketMatches[0];
        }

        return null;
    } catch {
        return null;
    }
};

I try to create a unit-test for this function:

import { getTicketIdFromBranchName } from '@/utils/git-info';

const TICKET_ID_REGEX = /((?<!([A-Z]{1,10})-?)[A-Z]+-\d+)/.source;

describe('[utils/git-info]', () => {
    it('getTicketIdFromBranchName | Function should proper ticket Id when there is one', async () => {
        const ticketId = 'CLO-1234';

        jest.mock('simple-git', () => {
            const mGit = {
                branchLocal: jest.fn(() => Promise.resolve({ current: `${ticketId} DUMMY TEST` })),
            };

            return jest.fn(() => mGit);
        });

        const result = await getTicketIdFromBranchName(new RegExp(TICKET_ID_REGEX));

        expect(result === ticketId).toEqual(true);
    });
});

But the unit-test fails. I says I expected to get true but it got false in the final line.

I guess I use jest.mock in the wrong way.

Answer 1

The official documentation has a key description of the use of jest.mock .

Note: In order to mock properly, Jest needs jest.mock('moduleName') to be in the same scope as the require/import statement.

You call the jest.mock('moduleName') inside test case function scope, but import the git-info module in module scope. That's why mock doesn't work.

Use require('moduleName') or await import('moduleName') in test case function. The order of the require/import and jest.mock() statements does not matter.

git-info.js :

import simpleGit from 'simple-git';

/**
 * The function returns the ticket Id, is presents, in the branch name
 * @returns ticket Id
 */
export const getTicketIdFromBranchName = async (ticketRegex) => {
  const git = simpleGit();

  try {
    const localBranches = await git.branchLocal();
    const currentBranch = localBranches.current;
    const currentBranchTicketMatches = currentBranch.match(ticketRegex);

    if (currentBranchTicketMatches) {
      return currentBranchTicketMatches[0];
    }

    return null;
  } catch {
    return null;
  }
};

git-info.test.js :

const TICKET_ID_REGEX = /((?<!([A-Z]{1,10})-?)[A-Z]+-\d+)/.source;

describe('[utils/git-info]', () => {
  it('getTicketIdFromBranchName | Function should proper ticket Id when there is one', async () => {
    const { getTicketIdFromBranchName } = await import('./git-info');
    const ticketId = 'CLO-1234';

    jest.mock(
      'simple-git',
      () => {
        const mGit = {
          branchLocal: jest.fn(() => Promise.resolve({ current: `${ticketId} DUMMY TEST` })),
        };

        return jest.fn(() => mGit);
      },
      { virtual: true }
    );

    const result = await getTicketIdFromBranchName(new RegExp(TICKET_ID_REGEX));

    expect(result === ticketId).toEqual(true);
  });
});

Test result:

 PASS  stackoverflow/71808909/git-info.test.js (7.439 s)
  [utils/git-info]
    ✓ getTicketIdFromBranchName | Function should proper ticket Id when there is one (6892 ms)

-------------|---------|----------|---------|---------|-------------------
File         | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-------------|---------|----------|---------|---------|-------------------
All files    |   84.62 |       50 |     100 |   81.82 |                   
 git-info.js |   84.62 |       50 |     100 |   81.82 | 19-21             
-------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        8.215 s, estimated 9 s

package version: "jest": "^26.6.3"