CODEWITHSUNDEEP
javascriptnode.jsjestjs
Ali Khan
Ali Khan

Reputation: 134

How to throw error in an async function in jest

How do i test if the function createTempUsageStatisticsTable(athenaExpress) throws an error and also to test if createTempUsageStatisticsTable(athenaExpress) throws error because the function athenaExpress.query(athenaQueryParam) throws an error (Using Jest) ? (Assume filename to be index.js)

async function createTempUsageStatisticsTable(athenaExpress) {
  let athenaQueryParam = {
      sql: getSqlQueries.CREATE_DEVICE_USAGE_STATS_TEMP_TABLE_QUERY,
      db: "testdb"
  };
      await athenaExpress.query(athenaQueryParam);
}
exportFunctions={createTempUsageStatisticsTable:createTempUsageStatisticsTable}

module.exports=exportFunctions

Now,I want to write a test to test if createTempUsageStatisticsTable(athenaExpress) throws an error when athenaExpress.query(athenaQueryParam)throws an error or rejects a promise in a mock implementation whichever is suitable or works,so i did

    const confError = new Error('network error');
    athenaExpress.query = jest.fn().mockImplementationOnce(() => {
        throw new Error(confError);    // tried this 
        promise.reject(confError);
    })
    index.configureAthenaExpress();
    expect(index.configureAthenaExpress).toThrow();

However tests do not seem to pass please help

Thanks to James i got it working,However i slightly tweaked his code as i was getting some error due to strict equal,The code is as follows:

test("createTempUsageStatisticsTable throws an exception if 
    athenaExpress.query fails()", async () => {

    const creaError=new Error("network error")
    athenaExpress=configureAthenaExpress();
    athenaExpress.query.mockRejectedValueOnce(creaError);
    await expect(createTempUsageStatisticsTable(athenaExpress)).rejects.toBe(creaError);
  });

Upvotes: 2

Views: 15240

Answers (1)

James
James

Reputation: 82136

Depending on how athenaExpress is exported, you can mock query to throw and then test for the existence of said by leveraging rejects e.g. 

const createTempUsageStatisticsTable = require("./createTempUsageStatisticsTable");
const athenaExpress = require("./athenaExpress");

jest.mock("./athenaExpress");

test("createTempUsageStatisticsTable throws if query fails", async () => {
  athenaExpress.query.mockRejectedValueOnce(new Error("network error"));
  await expect(createTempUsageStatisticsTable(athenaExpress)).rejects.toMatchObject({ message: "network error" });
});

Upvotes: 4

Related Questions