Unit Test with TryUpdateModelAsync fails with argument null exception Parameter name: metadataProvider

[Rudy James]

Is this a Bug or Feature request?:

Bug

Steps to reproduce (preferably a link to a GitHub repo with a repro project):

`
[HttpPatch("{id}")]
[ProducesResponseType(typeof(IDictionary<string, string>), (int)HttpStatusCode.BadRequest)]
[ProducesResponseType((int)HttpStatusCode.BadRequest)]
[ProducesResponseType((int)HttpStatusCode.NotFound)]
[ProducesResponseType((int)HttpStatusCode.NoContent)]
[ProducesResponseType((int)HttpStatusCode.InternalServerError)]
[Consumes(Constants.JsonPatch)]

    public async Task<IActionResult> Patch(int id, [FromBody, Required] JsonPatchDocument<MyDto> myDto)
    {
        try
        {
            var  original = new MyDto();
            myDto.ApplyTo(original);
            
            if(!await TryUpdateModelAsync<MyDto>(original))
            {
                return BadRequest(ModelState);
            }                
        }
        catch (Exception e)
        {
            logger.LogError(e, string.Empty);
            return StatusCode((int)HttpStatusCode.InternalServerError, e);
        }

        return NoContent();
    }`

Description of the problem:

The above code executes fine but when manual testing but my unit test method fails with argument null exception Parameter name: metadataProvider when calling TryUpdateModelAsync method.

Version of Microsoft.AspNetCore.Mvc or Microsoft.AspNetCore.App or Microsoft.AspNetCore.All:

Microsoft.AspNetCore.App version 2.1.1

[Artak]

@rrjamesjr, please share with us the project so we can repro the unit-test failure.

[Rudy James]

Here is the repo

https://github.com/rrjamesjr/Issue8721

[Artak]

@rrjamesjr, looks like you haven't properly configured the ValueProviderFactories of the ControllerContext for the controller being tested:

The ControllerBase.TryUpdateModelAsync method delegates the work to

Mvc/src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/ModelBindingHelper.cs

Line 206 in bf8058d

 public static async Task<bool> TryUpdateModelAsync( 

which in turn requires the modelMetadataProvider to be available.

@pranavkm, do we have a sample which would showcase how to do this properly?

[Pranav K]

If you'd like to unit test your controller action, I'd go the route of stubbing ControllerBase.TryUpdateModelAsync to verify if it does the right thing. If you're looking for an integration style test where the framework method executes as is, https://docs.microsoft.com/en-us/aspnet/core/test/integration-tests?view=aspnetcore-2.1 has pretty detailed documentation on how you'd set this up.

[Rudy James]

Thanks...just mocked the controller and stubbed the method as suggested