Add unit tests for create file upload API

Src/Notion.Client/Api/FileUploads/Create/Request/CreateFileUploadRequest.cs

@@ -4,7 +4,7 @@ public class CreateFileUploadRequest : ICreateFileUploadBodyParameters
     {
         public FileUploadMode Mode { get; set; }
 
-        public string Filename { get; set; }
+        public string FileName { get; set; }
 
         public string ContentType { get; set; }
 

Src/Notion.Client/Api/FileUploads/Create/Request/ICreateFileUploadBodyParameters.cs

@@ -20,7 +20,7 @@ public interface ICreateFileUploadBodyParameters
         /// from the content_type parameter.
         /// </summary>
         [JsonProperty("filename")]
-        string Filename { get; }
+        string FileName { get; }
 
         /// <summary>
         /// MIME type of the file to be created. Recommended when sending the file in multiple parts. 

Test/Notion.IntegrationTests/FIleUploadsClientTests.cs

@@ -14,7 +14,7 @@ public async Task CreateAsync()
             {
                 Mode = FileUploadMode.ExternalUrl,
                 ExternalUrl = "https://unsplash.com/photos/hOhlYhAiizc/download?ixid=M3wxMjA3fDB8MXxhbGx8fHx8fHx8fHwxNzYwMTkxNzc3fA&force=true",
-                Filename = "sample-image.jpg",
+                FileName = "sample-image.jpg",
             };
 
             // Act

Test/Notion.UnitTests/FileUploadClientTests.cs

@@ -0,0 +1,70 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Moq;
+using Moq.AutoMock;
+using Newtonsoft.Json;
+using Notion.Client;
+using Xunit;
+
+namespace Notion.UnitTests;
+
+public class FileUploadClientTests
+{
+    private readonly AutoMocker _mocker = new();
+    private readonly FileUploadsClient _fileUploadClient;
+    private readonly Mock<IRestClient> _restClientMock;
+
+    public FileUploadClientTests()
+    {
+        _restClientMock = _mocker.GetMock<IRestClient>();
+        _fileUploadClient = _mocker.CreateInstance<FileUploadsClient>();
+    }
+
+    [Fact]
+    public async Task CreateAsync_ThrowsArgumentNullException_WhenRequestIsNull()
+    {
+        // Act & Assert
+        var exception = await Assert.ThrowsAsync<ArgumentNullException>(() => _fileUploadClient.CreateAsync(null));
+        Assert.Equal("fileUploadObjectRequest", exception.ParamName);
+        Assert.Equal("Value cannot be null. (Parameter 'fileUploadObjectRequest')", exception.Message);
+    }
+
+    [Fact]
+    public async Task CreateAsync_CallsRestClientPostAsync_WithCorrectParameters()
+    {
+        // Arrange
+        var request = new CreateFileUploadRequest
+        {
+            FileName = "testfile.txt",
+            Mode = FileUploadMode.SinglePart,
+        };
+
+        var expectedResponse = new CreateFileUploadResponse
+        {
+            UploadUrl = "https://example.com/upload",
+            Id = Guid.NewGuid().ToString(),
+        };
+
+        _restClientMock
+            .Setup(client => client.PostAsync<CreateFileUploadResponse>(
+                It.Is<string>(url => url == ApiEndpoints.FileUploadsApiUrls.Create()),
+                It.IsAny<ICreateFileUploadBodyParameters>(),
+                It.IsAny<IEnumerable<KeyValuePair<string, string>>>(),
+                It.IsAny<IDictionary<string, string>>(),
+                It.IsAny<JsonSerializerSettings>(),
+                It.IsAny<IBasicAuthenticationParameters>(),
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(expectedResponse);
+
+        // Act
+        var response = await _fileUploadClient.CreateAsync(request);
+
+        // Assert
+        Assert.Equal(expectedResponse.UploadUrl, response.UploadUrl);
+        Assert.Equal(expectedResponse.Id, response.Id);
+
+        _restClientMock.VerifyAll();
+    }
+}