TypeError: Cannot read property 'getContext' of null

I have created a game using canvas API and now I am testing using Jest. But when running a test for a simple function it throws me this error. my script tag is at the end of the HTML and I also added this event listener to wait for the DOM document.addEventListener("DOMContentLoaded", init,false);

jest

PASS tests/sum.test.js FAIL tests/mod.test.js ● Test suite failed to run

TypeError: Cannot read property 'getContext' of null

  20 |   const empty = 0;
  21 |   const nextPieceCanvas = document.querySelector("canvas#nextPiece") as HTMLCanvasElement;
> 22 |   const NPctx = nextPieceCanvas.getContext("2d")! as CanvasRenderingContext2D;
     |                               ^
  23 |   
  24 |   //Gameboard Canvas
  25 |   const canvas = document.querySelector("canvas#tetris") as HTMLCanvasElement;

  at Object.<anonymous> (src/ts/app.ts:22:31)
  at Object.<anonymous> (tests/mod.test.js:2:1)

Test Suites: 1 failed, 1 passed, 2 total Tests: 1 passed, 1 total Snapshots: 0 total Time: 1.424 s Ran all test suites. npm ERR! code ELIFECYCLE npm ERR! errno 1 npm ERR! tetris_ts@1.0.0 test: jest npm ERR! Exit status 1 npm ERR! npm ERR! Failed at the tetris_ts@1.0.0 test script. npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in: npm ERR! /home/alex/.npm/_logs/2021-02-26T22_46_02_771Z-debug.logenter code here