How to access in `this.owner` as a property in Ember js test?

I added an ember adapter with some extra logic, then I would like to test that logic in ember test.

In the test file, I see this line repeated multiple times let adapter = this.owner.lookup('adapter:assessment'); inside each test.

I would like to move that line into a class level attribute for accessing my adapter. How do I do that? I think it has something to do with this.owner.lookup is only accessible within test().

(Using ember js 3.2.6)

import { module, test } from 'qunit';
import { setupTest } from 'ember-qunit';

module('Unit | Adapter | assessment', function (hooks) {
  setupTest(hooks);
  let myVar = 'abc';
  let adapterVar = this.owner.lookup('adapter:assessment'); // This fails! How to do this correctly?

  test('it exists', function (assert) {
    let adapter = this.owner.lookup('adapter:assessment');
    console.log(myVar); // This works!
    assert.ok(adapter);
  });

  test('Test 1', function (assert) {
    let adapter = this.owner.lookup('adapter:assessment');
    console.log(myVar);      // This works!
    console.log(adapterVar); // This fails!
    assert.ok(adapter);
  });

  test('Test 2', function (assert) {
    let adapter = this.owner.lookup('adapter:assessment');
    console.log(myVar);      // This works!
    console.log(adapterVar); // This fails!
    assert.ok(adapter);
  });

  test('Test 3', function (assert) {
    let adapter = this.owner.lookup('adapter:assessment');
    console.log(myVar);      // This works!
    console.log(adapterVar); // This fails!
    assert.ok(adapter);
  });

});