React Testing Error : TestingLibraryElementError: Unable to find an element with the text

I am using React Testing Library for first time and it seems very confusing. I am stuck on the error since long. I will be very grateful if someone proposes a solution to this problem

Here is my testfile:

import React from 'react';
import { cleanup, fireEvent, screen } from '@testing-library/react';
import { act } from 'react-dom/test-utils';
import { render } from '../../../test-util';
import EmailEditor from '../../../../components/commonComponents/EmailInput/EmailChip';


const mockFn = jest.fn();

const props={
    salutation: '',
    signature: '',
    emailBody: '',
    onChangeEmailBody: () => { },
    onFocus: () => { },
    onBlur: () => { },
    disabled: false,
    showSalutation: true,
    showSignature: true,
    allowVariables: false,
    showPersonalize: false,
    customParams: [],
    recommendImgSize: '',
    autoFocus: false,
    allowFonts: true
}



describe('Email Editor Test cases', () => {
    afterEach(cleanup);
  
    it('Determining the ', async () => {
      act(() => {
        render(<EmailEditor {...props} /> );
      });
      const OnclickElement = screen.getByText(/Select Personalization Parameter/i)
      expect(OnclickElement).toBeInTheDocument();
    });

    it('should render the button', async () => {
        act(() => {
          render(<EmailEditor {...props} /> );
        });
        const OnclickElement = screen.getByTestId(/custom/i)
        expect(OnclickElement).toBeInTheDocument();
      });

  

Here are some of the elements which are associated in index.js

<Header style={{ fontSize: window.innerWidth > MOBILE_WIDTH ? '1.15vw' : 12.15 }}>Select Personalization Parameter</Header>

<CustomToolbar key="customToolbar" show={allowVariables && showPersonalize} uniqueKey={uniqueKey} recommendImgSize={recommendImgSize} allowFonts={allowFonts} data-testid = "custom"/>

Please help me with this.