Model State Validation

01-ValidCall

C:\Users\jberube>http get localhost:53043/api/MyModels/10
HTTP/1.1 200 OK
Cache-Control: no-cache
Content-Length: 12
Content-Type: application/json; charset=utf-8
Date: Tue, 01 Nov 2016 20:50:32 GMT
Expires: -1
Pragma: no-cache
Server: Microsoft-IIS/10.0
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
X-SourceFiles: =?UTF-8?B?YzpcdXNlcnNcamJlcnViZVxkb2N1bWVudHNcdmlzdWFsIHN0dWRpbyAyMDE1XFByb2plY3RzXFdlYkFwcGxpY2F0aW9uMTZcV2ViQXBwbGljYXRpb24xNlxhcGlcTXlNb2RlbHNcMTA=?=

{
    "Value": 10
}

02-InvalidCall

C:\Users\jberube>http get localhost:53043/api/MyModels/101
HTTP/1.1 400 Bad Request
Cache-Control: no-cache
Content-Length: 0
Date: Tue, 01 Nov 2016 20:50:46 GMT
Expires: -1
Pragma: no-cache
Server: Microsoft-IIS/10.0
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
X-SourceFiles: =?UTF-8?B?YzpcdXNlcnNcamJlcnViZVxkb2N1bWVudHNcdmlzdWFsIHN0dWRpbyAyMDE1XFByb2plY3RzXFdlYkFwcGxpY2F0aW9uMTZcV2ViQXBwbGljYXRpb24xNlxhcGlcTXlNb2RlbHNcMTAx?=

MyModel.cs

public class MyModel
{
    public const int MaximumValue = 100;
    public const int MinimumValue = 1;

    [Range(MinimumValue, MaximumValue)]
    public int Value { get; set; }
}

MyModelsController.cs

public class MyModelsController : ApiController
{
    [Route("api/MyModels/{Value}")]
    public IHttpActionResult Get([FromUri]MyModel model)
    {
        if (!ModelState.IsValid)
            return BadRequest();

        return Ok(model);
    }
}

MyModelsControllerTests.cs

[Fact]
public void GetReturnsBadRequestForInvalid()
{
    var target = new MyModelsController();

    target.ModelState.AddModelError("*", "Anything goes wrong");

    IHttpActionResult actual = target.Get(null);

    Assert.IsType<BadRequestResult>(actual);
}

[Fact]
public void GetReturnsOKAndModelForValid()
{
    var target = new MyModelsController();

    var expected = new MyModel();

    IHttpActionResult result = target.Get(expected);
    var okResult = Assert.IsType<OkNegotiatedContentResult<MyModel>>(result);

    Assert.Same(expected, okResult.Content);
}

MyModelTests.cs

static MyModel CreateValid() => new MyModel
{
    Value = MyModel.MinimumValue
};

[InlineData(MyModel.MaximumValue)]
[InlineData(MyModel.MaximumValue - 1)]
[InlineData(MyModel.MaximumValue - 10)]
[InlineData(MyModel.MinimumValue + 10)]
[InlineData(MyModel.MinimumValue + 1)]
[InlineData(MyModel.MinimumValue)]
[Theory]
public void InRangeIsValid(int value)
{
    var target = CreateValid();
    target.Value = value;

    bool actual = ValidationTest.IsValid(target);
    Assert.True(actual, "MyModel is invalid when in range.");
}

[InlineData(MyModel.MaximumValue + 1)]
[InlineData(MyModel.MinimumValue - 1)]
[InlineData(int.MaxValue)]
[InlineData(int.MinValue)]
[Theory]
public void OutOfRangeIsInvalid(int value)
{
    var target = CreateValid();
    target.Value = value;

    bool actual = ValidationTest.IsValid(target);
    Assert.False(actual, "MyModel is valid when out of range.");
}