c# - How to mock an IFormFile for a unit/integration test in ASP.NET Core?

Question

I want to write tests for uploading of files in ASP.NET Core but can't seem to find a nice way to mock/instantiate an object derived from IFormFile.

Any suggestions on how to do this?

Answer 1

Assuming you have a Controller like..

public class MyController : Controller {
    public Task<IActionResult> UploadSingle(IFormFile file) {...}
}

...where the IFormFile.OpenReadStream() is accessed with the method under test.

You can create a test using Moq mocking framework to simulate the stream data.

[TestClass]
public class IFormFileUnitTests {
    [TestMethod]
    public async Task Should_Upload_Single_File() {
        //Arrange
        var fileMock = new Mock<IFormFile>();
        //Setup mock file using a memory stream
        var content = "Hello World from a Fake File";
        var fileName = "test.pdf";
        var ms = new MemoryStream();
        var writer = new StreamWriter(ms);
        writer.Write(content);
        writer.Flush();
        ms.Position = 0;
        fileMock.Setup(_ => _.OpenReadStream()).Returns(ms);
        fileMock.Setup(_ => _.FileName).Returns(fileName);
        fileMock.Setup(_ => _.Length).Returns(ms.Length);

        var sut = new MyController();
        var file = fileMock.Object;

        //Act
        var result = await sut.UploadSingle(file);

        //Assert
        Assert.IsInstanceOfType(result, typeof(IActionResult));
    }
}

Or, as of ASP.NET Core 3.0, use an instance of the FormFile Class which is now the default implementation of IFormFile.

Here is an example of the same test above using FormFile class

[TestClass]
public class IFormFileUnitTests {
    [TestMethod]
    public async Task Should_Upload_Single_File() {
        //Arrange
       
        //Setup mock file using a memory stream
        var content = "Hello World from a Fake File";
        var fileName = "test.pdf";
        var stream = new MemoryStream();
        var writer = new StreamWriter(stream);
        writer.Write(content);
        writer.Flush();
        stream.Position = 0;

        //create FormFile with desired data
        IFormFile file = new FormFile(stream, 0, stream.Length, "id_from_form", fileName);
        
        MyController sut = new MyController();
        
        //Act
        var result = await sut.UploadSingle(file);

        //Assert
        Assert.IsInstanceOfType(result, typeof(IActionResult));
    }
}