C# Online Compiler | .NET Fiddle

using System;
using System.Linq;
using System.Net.Http;
using System.Threading.Tasks;
using FluentAssertions;
using Flurl;
using Flurl.Http;
using Flurl.Http.Testing;
					
public class Program
{
	static async Task Main(string[] args)
        {
            await TestGetData();
        }
	
	 public static async Task TestGetData()
        {
            using (var httpTest = new HttpTest())
            {
                httpTest.RespondWith("json result", 200);
                
                var result = await GetData();

                httpTest.ShouldHaveCalled("https://flurltestservice.azurewebsites.net/v2/users?AccessToken=token&ResultsCounts=20&q=Tomasz%20%C5%BByrek#Results")
                    .WithVerb(HttpMethod.Get)
                    .Times(1);

                result
                    .Should()
                    .Be("json result");
				
				Console.WriteLine("Test completed.");
            }
        }
	
	private static async Task<string> GetData()
        {
            var result = await "https://flurltestservice.azurewebsites.net/"
                .AppendPathSegment("v2")
                .AppendPathSegment("users")
                .SetQueryParams(new
                {
                    AccessToken = "token",
                    ResultsCounts = 20,
                    q = "Tomasz Żyrek"
                })
                .SetFragment("Results")
                .GetAsync()
                .ReceiveString();

            return result;
        }
}

 
using System;
using System.Linq;
using System.Net.Http;
using System.Threading.Tasks;
using FluentAssertions;
using Flurl;
using Flurl.Http;
using Flurl.Http.Testing;
                    
public class Program
{
    static async Task Main(string[] args)
        {
            await TestGetData();
        }
    
     public static async Task TestGetData()
        {
            using (var httpTest = new HttpTest())
            {
                httpTest.RespondWith("json result", 200);
                
                var result = await GetData();
​

Unhandled exception. FluentAssertions.Execution.AssertionFailedException: Expected string to be
"https://flurltestservice.azurewebsites.net/v2/users?AccessToken=token&ResultsCounts=20" with a length of 86, but
"https://flurltestservice.azurewebsites.net/v2/users?AccessToken=token&ResultsCounts=20&q=Tomasz%20%C5%BByrek#Results" has a length of 116, differs near "&q=" (index 86).
   at FluentAssertions.Execution.FallbackTestFramework.Throw(String message) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\FallbackTestFramework.cs:line 18
   at FluentAssertions.Execution.TestFrameworkProvider.Throw(String message) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\TestFrameworkProvider.cs:line 40
   at FluentAssertions.Execution.DefaultAssertionStrategy.HandleFailure(String message) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\DefaultAssertionStrategy.cs:line 29
   at FluentAssertions.Execution.AssertionScope.FailWith(Func`1 failReasonFunc) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\AssertionScope.cs:line 223
   at FluentAssertions.Execution.AssertionScope.FailWith(Func`1 failReasonFunc) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\AssertionScope.cs:line 196
   at FluentAssertions.Primitives.StringEqualityValidator.ValidateAgainstLengthDifferences() in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Primitives\StringEqualityValidator.cs:line 31
   at FluentAssertions.Primitives.StringValidator.Validate() in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Primitives\StringValidator.cs:line 41
   at FluentAssertions.Primitives.StringAssertions.Be(String expected, String because, Object[] becauseArgs) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Primitives\StringAssertions.cs:line 39
   at HttpCallAssertionExtensions.ShouldHaveExactCall(HttpTest test, String exactUrl)
   at Program.TestGetData()
   at Program.Main(String[] args)
   at Program.<Main>(String[] args)
Command terminated by signal 6