Mock An IFormFile for a Unit/Integration Test In ASP.NET Core

I've developed an ASP.NET Core API project for my Angular client. Now, I'm in the process of writing integration tests to validate the file upload functionality in my endpoints, which is responsible for updating user profile data, within my user profile controller, I'm utilizing the IFormFile interface to handle file uploads.

However, I'm unsure of how to mock an IFormFile object for unit and integration testing purposes in ASP.NET Core.

If you're also facing a similar challenge and looking for a solution for this task, I recommend reading rhis article in that you can find the answer to your question. This post provides detail understading into how to mock or instantiate an object derived from IFormFile for testing file uploads in ASP.NET Core.

When testing ASP.NET Core controllers that handle file uploads, such as a UserProfileController with a profile picture upload feature, we many times need to mock an IFormFile object to simulate file uploads in unit or integration tests. Here's how we can achieve this task:

First, let's create a UserProfileController with an action method for updating user profiles:

[HttpPost]
public async Task<IActionResult> UpdateProfile(int userId, string firstName, string lastName, IFormFile profilePicture)
{
    try
    {
        // Get user from the database
        var user = await _context.Users.FindAsync(userId);
        if (user == null)
        {
            return NotFound(); // User not found
        }

        // Update user's first name and last name
        user.FirstName = firstName;
        user.LastName = lastName;

        // Check if a new profile picture is provided
        if (profilePicture != null && profilePicture.Length > 0)
        {
            // Save the new profile picture
            // Logic to handle file upload and storage can be implemented here
            // For example, saving the file to a specified directory or cloud storage
            // You may use libraries like Azure Blob Storage SDK or File System APIs

            // For example , let's assume we save the profile picture to a directory named "ProfilePictures"
            var profilePicturePath = Path.Combine("ProfilePictures", Guid.NewGuid().ToString() + Path.GetExtension(profilePicture.FileName));
            using (var stream = new FileStream(profilePicturePath, FileMode.Create))
            {
                await profilePicture.CopyToAsync(stream);
            }

            // Update user's profile picture path in the database
            user.ProfilePicturePath = profilePicturePath;
        }

        // Update user in the database
        _context.Users.Update(user);
        await _context.SaveChangesAsync();

        return Ok(); // Profile updated successfully
    }
    catch (Exception ex)
    {
        // Log the exception or handle it appropriately
        return StatusCode(StatusCodes.Status500InternalServerError, "An error occurred while updating the user profile.");
    }
}

Next, let's create a unit test using xUnit and Moq to mock the IFormFile object:

In this unit test, we create a MemoryStream to simulate the file content,  we mock the IFormFile object using Moq and set up its properties and behavior and then, we invoke the action method of the UserProfileController and verify the expected behavior.

  public class UserProfileControllerTests
  {
      [Fact]
      public async Task UpdateProfile_ShouldUpdateUserProfile()
      {
          // Arrange
          var userId = 1;
          var firstName = "John";
          var lastName = "Doe";
          var profilePictureFileName = "profile.jpg";
          var profilePictureStream = new MemoryStream();
          // Write dummy data to the stream if needed

          var formFileMock = new Mock<IFormFile>();
          formFileMock.Setup(f => f.FileName).Returns(profilePictureFileName);
          formFileMock.Setup(f => f.Length).Returns(profilePictureStream.Length);
          formFileMock.Setup(f => f.CopyToAsync(It.IsAny<Stream>()))
                      .Returns((Stream destination) => 
                      {
                          profilePictureStream.CopyTo(destination);
                          return Task.CompletedTask;
                      });

          var controller = new UserProfileController(CreateMockUserDbContext().Object);

          // Act
          var result = await controller.UpdateProfile(userId, firstName, lastName, formFileMock.Object);

          // Assert
          // Add your assertions here
      }

      private Mock<UserDbContext> CreateMockUserDbContext()
      {
          // Implement mock UserDbContext if needed
      }
  }
  

We create a function named GetProfilePictureMock to generate a mock IFormFile for simulating profile picture uploads, that takes parameters for the content type of the image (contentType) and the byte array representing the image content. 

And this function convert the image content to a byte array and use it to create a MemoryStream, which serves as the base stream for the FormFile. 

We createa new FormFile object with the MemoryStream, specifying the name and file name as "ProfilePicture" and "dumyprofile.jpg", we set the content type of the FormFile and return it. 

This function can be used in your unit tests to simulate profile picture uploads for testing the UpdateProfile action method in the UserProfileController.

private IFormFile GetProfilePictureMock(string contentType, byte[] content)
{
    var file = new FormFile(
        baseStream: new MemoryStream(content),
        baseStreamOffset: 0,
        length: content.Length,
        name: "ProfilePicture",
        fileName: "dumyprofile.jpg"
    )
    {
        Headers = new HeaderDictionary(),
        ContentType = contentType
    };

    return file;
}

3

We can create an actual instance of the IFormFile interface using a simple approach like this,this solution provides a simple and straightforward way to create a mock IFormFile instance for testing purposes, it's important to note that the third parameter (length) in the FormFile constructor should be greater than 0 to ensure that the file has a non-zero length. Otherwise, the Length property of the file will be zero.

    bytes[] filebytes = Encoding.UTF8.GetBytes("image");
    IFormFile file = new FormFile(new MemoryStream(filebytes), 0, filebytes.Length, "Data", "profileimage.png");
  

This approach is useful when we need to quickly create mock instances of IFormFile for unit  testing where we don't need to simulate actual file content.

4 Let's see how we can mock an IFormFile for a unit or integration test in ASP.NET Core when uploading an image to blob storage:

using Microsoft.AspNetCore.Http;
using System.IO;
using System.Text;

public class UserProfileControllerTests
{
    [Fact]
    public async Task UploadImageToBlobStorage_ShouldUploadImageSuccessfully()
    {
        // Arrange
        var userId = 1;
        var firstName = "John";
        var lastName = "Doe";
        var profilePictureFileName = "profile.jpg";
        var profilePictureContent = Encoding.UTF8.GetBytes("image content");

        // Mock IFormFile
        var profilePictureStream = new MemoryStream(profilePictureContent);
        var profilePicture = new FormFile(profilePictureStream, 0, profilePictureContent.Length, "Data", profilePictureFileName);

        var blobStorageMock = new Mock<IBlobStorageService>();
        // Configure the blob storage mock as needed for testing

        var controller = new UserProfileController(CreateMockUserDbContext().Object, blobStorageMock.Object);

        // Act
        var result = await controller.UploadImageToBlobStorage(userId, firstName, lastName, profilePicture);

        // Assert
        
    }

    private Mock<UserDbContext> CreateMockUserDbContext()
    {
        
    }
}