Unit test exercise on how to test REST API

TestLanguageToolAPI

using System.Net;
using System.Net.Mime;
using NUnit.Framework;
using RestSharp;

namespace UnitTestsExercise
{
    [Category("Integration")]
    [Category("Rest")]
    public class UnitTest1
    {
        [Test]
        public void TestMethodPositive1()
        {
            var client = new RestClient("https://languagetool.org");
            var request = new RestRequest("/api/v2/languages", Method.GET);
            var response = client.Execute<LanguageModel>(request);

            Assert.That(response, Is.Not.Null, "Response couldn't be deserialized");
            Assert.That(response.StatusCode, Is.EqualTo(HttpStatusCode.OK), "Unexpected HTTP status code");

        }

        [Test]
        public void TestMethodNegative1()
        {
            var client = new RestClient("https://languagetool.org");
            var request = new RestRequest("/api/v2/languages", Method.GET);
            var response = client.Execute<LanguageModel>(request);

            Assert.That(response, Is.Not.Null, "Response couldn't be deserialized");
            Assert.That(response.StatusCode, Is.Not.EqualTo(HttpStatusCode.Forbidden), "Unexpected HTTP status code");

        }

        [Test]
        //Test when text and data are empty
        public void WhenRequiredFieldIsEmpty()
        {
            var client2 = new RestClient("https://languagetool.org");
            var request2 = new RestRequest("/api/v2/check", Method.POST);
            var response2 = client2.Execute<LanguageModel>(request2);

            Assert.That(response2, Is.Not.Null, "Response couldn't be deserialized");
            Assert.That(response2.StatusCode, Is.EqualTo(HttpStatusCode.InternalServerError), "Unexpected HTTP status code");
        }

        [Test]
        //Test when text field is not empty and data is empty
        public void WhenRequiredFieldIsNotEmpty()
        {
            var client3 = new RestClient("https://languagetool.org");
            var request3 = new RestRequest("/api/v2/check", Method.POST);
            request3.AddHeader("Content-Type", "application/x-www-form-urlencoded");
            request3.AddHeader("Accept", "application/json");

            request3.AddParameter("text", "test");
            request3.AddParameter("language", "en-US");
            request3.AddParameter("enabledOnly", "false");

            var response3 = client3.Execute<LanguageModel>(request3);

            Assert.That(response3.Content, Is.Not.Null, "Test");
            Assert.That(response3, Is.Not.Null, "Response couldn't be deserialized");
            Assert.That(response3.StatusCode, Is.EqualTo(HttpStatusCode.OK), "Unexpected HTTP status code " + response3.StatusCode);
        }
    }
}