Question

I have a mocked class of a node module and its method as below, and test case to test case I need to change the methodOne returning value.

jest.mock("module_name", () => {
  return {
    __esModule: true,
    Abc: class Abc {
      constructor(config) {}

      async methodOne(params) {
        return {
          message: {
            content:
               This text I need to change ,
          },
        };
      }
    },
    Configuration: class Configuration {
      constructor(config) {
        return true;
      }
    },
  };
});

describe("getVeganStatus", () => {
  it("should handle case one......", async () => {
    // methodOne message.content return value should be "ABC"
  })

  it("should handle case two......", async () => {
    // methodOne message.content return value should be "XYZ"
  });
})```

Answer 1

Following Replacing the mock using mockImplementation() or mockImplementationOnce() documentation.

Calls to jest.mock are hoisted to the top of the code. You can specify a mock later, e.g. in beforeAll(), by calling mockImplementation() (or mockImplementationOnce()) on the existing mock instead of using the factory parameter. This also allows you to change the mock between tests, if needed:

E.g.

some-module.js:

export class Abc {
  constructor(config) {}

  async methodOne(params) {
    return {
      message: {
        content:
           This text I need to change ,
      },
    };
  }
}

main.js:

import { Abc } from  ./some-module ;

export async function main() {
    const abc = new Abc();
    return abc.methodOne().then((res) => res.message.content);
}

main.test.js:

import { main } from  ./main ;
import { Abc } from  ./some-module ;

jest.mock( ./some-module );

describe( 76863882 , () => {
    test( should pass 1 , async () => {
        Abc.mockImplementation(() => {
            return {
                methodOne: async () => ({ message: { content:  ABC  } }),
            };
        });
        const actual = await main();
        expect(actual).toBe( ABC );
    });

    test( should pass 2 , async () => {
        Abc.mockImplementation(() => {
            return {
                methodOne: async () => ({ message: { content:  XYZ  } }),
            };
        });
        const actual = await main();
        expect(actual).toBe( XYZ );
    });
});

Test result:

 PASS  stackoverflow/76863882/main.test.js (5.787 s)
  76863882
    ✓ should pass 1 (2 ms)
    ✓ should pass 2

Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        5.978 s, estimated 6 s
Ran all test suites related to changed files.

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