Mocking functions at a very deeper level with jest

my file structure looks like below. I needed to mock a function which is three level deeper and not exported. Can someone help me figure out how to achieve this task please. My goal is not to send data to database.

file name c.js

exports.c.function3 = {
dbCall.then((data)=>data);
}

file name b.js

require("./c");
exports.b.function2 = ()=>{
c.function3()
.then((data)=>data);
}

filename - a.js

require("./b");
exports.function1 = ()=>{
b.function2()
.then((data)=>data);
}

file name - a.test.js
require("./a");
describe("Test cases a",()=>{


test("function1 should return data from db",()=>{
const dbCall = jest.spyOn(a,'function2.function3.dbCall');
dbCall.mockImplementation(()=>[1,2,3]);
function1.then((data)=>{
expect(data.length).toBe(3);
});
}
})

I tried multiple ways to mock the function, but none worked. Any help would be highly appreciated. Thanks.

You can do this in Jest with CJS by using jest.mock().

I do not understand your CJS imports and async flow 100%.
But this works, hope it helps:

c.js

const dbCall = () => {
    return new Promise((resolve, _reject) => resolve("Data from database"))
}

exports.function3 = () => {
    return dbCall().then((data) => data)
}

b.js

const c = require("./c");
exports.function2 = () => {
    return c.function3()
        .then((data) => data);
}

a.js

const b = require("./b");
exports.function1 = () => {
    return b.function2()
        .then((data) => data);
}

a.test.js

jest.mock('./c', () => {
    return {
        function3: jest.fn().mockReturnValue(
            new Promise((resolve, _reject) => resolve("Mocked data"))
        )
    };
});

const a = require("./a")

test("function1 should return data from db", () => {
    a.function1().then((data) => {
        expect(data).toBe("Mocked data");
    });
})

If you need the rest of c module intact, do like this:

jest.mock('./c', () => {
    const originalModule = jest.requireActual('./c')
    return {
        ...originalModule,
        function3: jest.fn().mockReturnValue(
            new Promise((resolve, _reject) => resolve("Mocked data"))
        )
    };
});

Result:

> 75891489@1.0.0 test
> jest

 PASS  ./a.test.js
  ✓ function1 should return data from db (2 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.265 s, estimated 1 s
Ran all test suites.

node: v18.12.1
jest: 29.5.0