Using jest-when to support parameterized mock return values

The jest library by itself currently doesn't support parameterized mock return values for Node.js unit tests, but it can by integrating the jest-when library.

Environment:
CentOS Linux release 7.3.1611 (Core)
node v8.16.0
jest 24.8.0
jest-when version 2.7.0

The below jest unit test example uses jest-when to have two different parameterized mock return values for a method (db.runQuery) that is called twice but has different return values to simulate two different database calls.

const runDbQuery = async(sql, params) => {
  // this is the external dependency call that needs to be mocked
  const dataSet = await db.runQuery(sql, params);
  return dataSet;
};

const retrieveData = async(params) => {
  const data1 = await runDbQuery(QUERY1, [params]);
  const data2 = await runDbQuery(QUERY2, [data1]);

  // some manipulation of data...
  const returnData = <some manipulation of data>;
  return returnData;
};


Unit test for unit:
const { when } = require('jest-when')

// import external dependencies for mocking
const db = require('./db');

const unit = require(<unit under test js file>)(db);

test('Test retrieveData', async () => {

  ///////////////////
  // db call 1 setup
  ///////////////////
  // first db.runQuery mock setup
  const params1_var1 = 5;
  const params1_var2 = "five";

  const paramsJson1 = JSON.stringify({
    params1_var1: params1_var1,
    params1_var2: params1_var2,
  });

  const params1 = [paramsJson1];

  const returnData1_var1 = 99;
  const returnData1_var2 = "ninety-nine";
  const returnData1_var3 = true;

  const returnData1 = [
  {
    returnData1_var1: returnData1_var1,
    returnData1_var2: returnData1_var2,
    returnData1_var3: returnData1_var3,
  }

  ];

  // format returned from db call
  const dataSets1 = {
    rows: returnData1,
  };

  const query1 = QUERY1;

  ///////////////////
  // db call 2 setup
  ///////////////////
  // second db.runQuery mock setup
  const params2_var1 = 22;

  const params2 = [params2_var1];

  // county query is different
  const query2 = QUERY2;

  const returnData2_var1 = 100;
  const returnData2_var2 = "one-hundred";

  const returnData2 = [
  {
    returnData2_var1: returnData2_var1,
    returnData2_var2: returnData2_var2
  }

  // format returned from db call
  const dataSets2 = {
    rows: returnData2,
  };

  / external dependency method call that needs to be mocked
  const mockDbRunQuery = db.runQuery = jest.fn().mockName('mockDbRunQuery');

  // first call to db.runQuery
  when(db.runQuery).calledWith(query1, params1).mockResolvedValue(dataSets1);

  // second call to db.runQuery
  when(db.runQuery).calledWith(query2, params2).mockResolvedValue(dataSets2);

  const retrieveDataReturnVal = {
  ...
  };

  await expect(unit.retrieveData(params)).resolves.toStrictEqual(retrieveDataReturnVal);

  // verify that mock method(s) were expected to be called
  expect(mockDbRunQuery).toHaveBeenCalledTimes(2);
});