1. 首先，安装相关的依赖：

npm install --save-dev jest graphql jest-graphql-mocks

2. 然后，编写一个名为mutation.test.js的测试文件，使用jest-graphql-mocks来模拟GraphQL请求和响应：

const { createMockedClient } = require('jest-graphql-mocks');
const { myMutation } = require('../myMutation');

describe('myMutation', () => {
  it('should call onSuccess callback when mutation is successful', async () => {
    const client = createMockedClient();
    client.setRequestHandler(myMutation, () => ({ data: { myMutation: true } }));

    const onSuccessMock = jest.fn();
    const onErrorMock = jest.fn();

    await myMutation({ client, onSuccess: onSuccessMock, onError: onErrorMock });

    expect(onSuccessMock).toHaveBeenCalledTimes(1);
    expect(onErrorMock).not.toHaveBeenCalled();
  });

  it('should call onError callback when mutation fails', async () => {
    const client = createMockedClient();
    client.setRequestHandler(myMutation, () => ({ errors: [{ message: 'Something went wrong' }] }));

    const onSuccessMock = jest.fn();
    const onErrorMock = jest.fn();

    await myMutation({ client, onSuccess: onSuccessMock, onError: onErrorMock });

    expect(onSuccessMock).not.toHaveBeenCalled();
    expect(onErrorMock).toHaveBeenCalledTimes(1);
  });
});

3. 最后，编写GraphQL Mutation的实现文件myMutation.js：

const MY_MUTATION = gql`
  mutation MyMutation {
    # Your mutation here
  }
`;

export function myMutation({ client, onSuccess, onError }) {
  return client
    .mutate({
      mutation: MY_MUTATION
    })
    .then(({ data }) => {
      onSuccess(data);
    })
    .catch(({ errors }) => {
      onError(errors);
    });
}

这样，我们就可以用Jest测试GraphQL Mutation的回调函数(onSuccess、onError)是否正确被调用了。