What is the best way to test a complex site?

Question

JavaScript

Good afternoon!
I came across this question: how will it be more correct and beautiful to test plugins in mocha.js?
Now I just generate tests through the forEach loop and run them, but it seems to me that this is not the most beautiful option:

[30, 18, 378, -9000].forEach(function (userLimit) {
  it(`should response valid chunked (limit: ${userLimit}) data `, async function () {
    const agent = request.agent(app);

    await agent
      .post('/rest/auth')
      .send({
        username,
        password
      });

    let users = [];
    let offset = 0;

    while (offset <= totalUserCount) {
      await agent
        .get('/rest/users')
        .query({
          limit: userLimit,
          offset: offset
        })
        .expect('Content-Type', /json/)
        .expect(200)
        .expect((res) => {
          const {body} = res;

          users = users.concat(body.data);

          if (userLimit < 1) {
            offset += 1;
          } else if (userLimit > 100) {
            offset += 100;
          } else {
            offset += userLimit;
          }
        });
    }

    expect(users).have.lengthOf(totalUserCount);
  });
});

If the cycle is pushed into the body, then the test will take a very long time. And it won’t work to shut up with a mock, because work with the base is partly tested.
In this case, how would it be more beautiful to rewrite this code, given that there is almost 90% repeatable test only without plugins, to check how REST behaves without parameters passed?