Skip to main content

Uniting Testing Expression Predicate with Moq

I recently was setting up a repository in a project with an interface on all repositories that took a predicate. As part of this I needed to mock out this call so I could unit test my code. The vast majority of samples out there for mocking an expression predicate just is It.IsAny<> which is not very helpful as it does not test anything other then verify it got a predicate. What if you actually want to test that you got a certain predicate though? It is actually pretty easy to do but not very straight forward.

Here is what you do for the It.IsAny<> approach in case someone is looking for that.

this.bindingRepository.Setup(c => c.Get(It.IsAny<Expression<Func<UserBinding, bool>>>())) 
.Returns(new List<UserBinding>() { defaultBinding }.AsQueryable());

This example just says to always return a collection of UserBindings that contain “defaultBinding” (which is an object I setup previously).

Here is what it looks like when you want to pass in an expression predicate that actually gets executed and only returns data if it matches something.

For my example I have a predicate that executes against an object collection of type “UserBinding.” The part to understand here is you are not passing to the Moq setup an expression. You are telling Moq to compile whatever expression it is given and see if that expression finds a match against the given object your provided. So in the example, does the expression passed in find a hit when executed against my “defaultBinding” object. If so return whatever data you want to return (in my case I am returning a collection of UserBindings as a queryable).

var defaultBinding = new UserBinding { Binding = new Binding { Name = "Default binding" }, Domain = "test.com" };
 
 
this.bindingRepository.Setup(c => c.Get(It.Is<Expression<Func<UserBinding, bool>>>(y => y.Compile()(defaultBinding))))
.Returns(new List<UserBinding>() { defaultBinding }.AsQueryable());

That is it. Now you can test expression predicates and return different out put based on the expression you are expecting to be passed in.

Comments

Anonymous said…
Very helpful. Thanks a lot, I was able to fix my tests.
Anonymous said…
Thanks, it saved my day as well !

Popular posts from this blog

Excel XIRR and C#

I have spend that last couple days trying to figure out how to run and Excel XIRR function in a C# application. This process has been more painful that I thought it would have been when started. To save others (or myself the pain in the future if I have to do it again) I thought I would right a post about this (as post about XIRR in C# have been hard to come by). Lets start with the easy part first. In order to make this call you need to use the Microsoft.Office.Interop.Excel dll. When you use this dll take note of what version of the dll you are using. If you are using a version less then 12 (at the time of this writing 12 was the highest version) you will not have an XIRR function call. This does not mean you cannot still do XIRR though. As of version 12 (a.k.a Office 2007) the XIRR function is a built in function to Excel. Prior version need an add-in to use this function. Even if you have version 12 of the interop though it does not mean you will be able to use the function. The

Password Management

The need to create, store and manage passwords is a huge responsibility in modern day life. So why is it that so many people do it so poorly? This is a loaded questions with answers ranging from people being uneducated, to lazy, to educated but not affective in their methods and many more. This blog is to help those (in some way even myself) around me strengthen their online security. Why does it matter? To answer this let's look at a few numbers. According to the US Department of Justice (DOJ)’s most recent study , 17.6 million people in the US experience some form of identity theft each year. Ok fine but that is identity theft that has nothing to do with password management. What is one way someone can start getting information about who you are? How do they get access to steal your money? From Cyber Security Ventures 2019 report : "Cybersecurity Ventures predicts that healthcare will suffer 2-3X more cyberattacks in 2019 than the average amount for other industries. W

WPF Localization - RESX Option

About a year ago I was building a WPF project in .Net 3.0 and Visual Studio 2005. I wanted to revisit this subject and see what has changed in .Net 3.5 and Visual Studio 2008. I will make a few of these posts to try and cover all the different options (RESX option, LocBaml option, Resource Dictionary Option). In this blog I will focus on using a resx file to localize an application. To show how the resx option is done I created a WPF form with three labels on it. The first label has is text set inline in XAML, the second has it text set via code behind from the resx file and the third has its text set via XAML accessing the resx file. The first thing that needs to happen to setup a project for localization is a small change to the project file. To make this change you will need to open the project file in notepad (or some other generic editor). In the first PropertyGroup section you need to add the follow XML node <UICulture>en-US</UICulture>. So the project file node w

MVVM light and Model Validation

I have been using the MVVM light toolkit for a project recently. It is a great toolkit but is missing a couple things and Laurent Bugnion does a good job trying to cover those holes. One of the things the toolkit does not support is Validation. The good news is there is a great CodePlex project out there call Fluent Validation that makes this pretty easy to add and really powerful. My objective was to add validation to my model so I could call “IsValid” on the model itself (similar to the MVC attribute approach). Fluent Validation has you create a new class file that holds you validation rules for a given model. This is the approach I took to enable each model to have an “IsValid” property and a “Errors” property that returns the validation errors. First I setup my ValidationFactory: public class ValidatorFactory : FluentValidation.ValidatorFactoryBase { public override FluentValidation.IValidator CreateInstance(Type validatorType) { return SimpleIoc.Default.G