Moq verify with object parameter

Question

I am trying to verify a parameter that is a class. The code being tested is fine. The bug is in the test.

I have tried two methods, both of which have failed.

Here are my attempts:

1:

this.MockImageResizeFilter.Verify(m => m.Filter(this.UploadedFileData, new ImageFilterOptions()
    {
        Width = 256,
        Height = 256,
    }));

This always fails, even though an object passed as the second parameter has equal properties. The first parameter is verified fine.

2:

this.MockImageResizeFilter.Setup(m => m.Filter(It.IsAny<byte[]>(), It.IsAny<ImageFilterOptions>()))
    .Callback<byte[], ImageFilterOptions>((data, options) =>
        {
            Assert.AreEqual(this.UploadedFileData, data, "data");
            Assert.AreEqual(filterOptions.Width, options.Width, "Width");
            Assert.AreEqual(filterOptions.Height, options.Height, "Height");
        }
    );

This always passes, even when it should fail. The Asserts in the callback do fail, but the exception is not passed to the outer context, and thus the test always passes.

Can you help me find what I am doing wrong?

score 202 · Accepted Answer · answered Nov 21 '12 at 15:30

The first attempt is closer to what you want to achieve.

The reason it fails is that Moq (probably) uses Object.Equals under the cover to test if the ImageFilterOptions parameter that the method was called with is the same instance as the one you supplied in the call to Verify.

It is impossible for them to be the same instance, because in Verify you create a new ImageFilterOptions().

Instead of performing the parameter check this way, you could use Moq's It.Is syntax to provide an expression that verifies the parameter was the expected one.

In your case, you want to check that the parameter is of type ImageFilterOptions and that both the Width and the Height are set to 256. The expression that allows you to do that is:

It.Is<ImageFilterOptions>(p => p.Width == 256 && p.Height == 256)

So, your call to Verify could look like this:

this.MockImageResizeFilter.Verify(m => m.Filter(
            this.UploadedFileData,
            It.Is<ImageFilterOptions>(p => p.Width == 256 && p.Height == 256)));

The syntax that I had to use would be: `It.Is((ImageFilterOptions p) => p.Width == 256 && p.Height == 256)`. There was no generic `Is` — Stanislav, Jul 21 '16 at 14:37
The generic version works for me and is in the API docs http://www.nudoq.org/#!/Packages/Moq/Moq/It/M/Is(TValue) - are you using an out of date version of Moq? — Tim Abell, Mar 22 '17 at 15:16

MarredCheese · Answer 2 · 2021-11-11T14:59:03.553

Moq's Verify method only tells you that the method was never called with the arguments you specified, with no explanation of which argument (or which property of an argument) was wrong. To get fine detail, use a callback to save the argument(s) to a variable and then assert against that:

ImageFilterOptions passedOptions = null;
this.MockImageResizeFilter.Setup(m => m.Filter(It.IsAny<byte[]>(), It.IsAny<ImageFilterOptions>()))
    .Callback<byte[], ImageFilterOptions>((data, options) =>
    {
        passedOptions = options
    });

// <exercise the mocked object>

this.MockImageResizeFilter.Verify(m => m.Filter(this.UploadedFileData, It.IsAny<ImageFilterOptions>());
Assert.AreEqual(expectedOptions.Width, passedOptions.Width, "Width");
Assert.AreEqual(expectedOptions.Height, passedOptions.Height, "Height");

// (If you wanted, you could also use the callback technique to check that
// `this.UploadedFileData` was passed in for the first parameter.)

This tells you exactly which argument/property was wrong.

You also get the opportunity to skip testing each property individually, which is nice when dealing with objects with many properties:

using FluentAssertions;

// ...

passedOptions.Should().BeEquivalentTo(expectedOptions);

(Note that BeEquivalentTo does point out individual property failures.)

Not being able to see which properties caused the failure has bugged me for a long time. Thanks for this! — adam0101, Jan 04 '23 at 21:00

Moq verify with object parameter

2 Answers2