[Fact]
public async Task Test()
{
    IImageManager imageManager = Substitute.For<IImageManager>();
    imageManager.FindByUrl(Arg.Any<string>())
        .Returns(callInfo => new ImageMetadataModel(callInfo.Arg<string>()));
}

public interface IFinder
{
    Task<string> GetTextAsync(string id);
}

public class Finder
{
    private readonly IFinder _finder;

    public Finder(IFinder finder)
    {
        _finder = finder;
    }

    public Task<string> GetTextAsync(string id)
    {
        return _finder.GetTextAsync(id);
    }
}

public class FinderTests
{
    [Fact]
    public async Task FinderTest1()
    {
        Finder finder = GetFinder();

        Assert.Equal(1, 1);
    }

    [Fact]
    public void FinderTest2()
    {
        int i = Arg.Any<int>(); // problem here

        Assert.Equal(1, 1);
    }

    private static Finder GetFinder()
    {
        IFinder internalFinder = Substitute.For<IFinder>();
        internalFinder.GetTextAsync(Arg.Any<string>()).Returns("text"); // fails here

        return new Finder(internalFinder);
    }
}