Unit test for the dummy cookie middleware

DummyCookieMiddlewareTests.cs

public class DummyCookieMiddlewareTests
{
    [Fact]
    public void GivenWebApp_WhenFirstRequestIsSentToWebApp_ThenDummyCookieIsAddedToResponse()
    {
        const string expectedOutput = "Request handed over to next request delegate";

        // Arrange
        DefaultHttpContext defaultContext = new DefaultHttpContext();
        defaultContext.Response.Body = new MemoryStream();
        defaultContext.Request.Path = "/";            

        // Act
        var middlewareInstance = new DummyCookieMiddleware(next: (innerHttpContext) =>
        {
            innerHttpContext.Response.WriteAsync(expectedOutput);
            return Task.CompletedTask;
        });

        middlewareInstance.Invoke(defaultContext);

        // Assert 1: if the next delegate was invoked
        defaultContext.Response.Body.Seek(0, SeekOrigin.Begin);
        var body = new StreamReader(defaultContext.Response.Body).ReadToEnd();
        Assert.Equal(expectedOutput, body);

        // Assert 2: if the cookie is added to the response
        var setCookieHeaders = defaultContext.Response.GetTypedHeaders().SetCookie;
        var cookie = setCookieHeaders?.FirstOrDefault(x => x.Name == "DummyCookie");
        Assert.True(Guid.TryParse(cookie.Value, out Guid result));
    }
}