Develop Reference

Unit Testing a Class With A Private Constructor

I am trying to test a class that only has a private constructor. This is for a course registration system. The courses do not get create via our application, therefore we intentionally have no public constructor. Instead we use EF to get the courses that are already in the database, and register students to them.
I am trying to test the register method of the Course class, however I have no way of creating an instance. I could use
course = (Course)Activator.CreateInstance(typeof(Course), true);, but then I don't have a way to setup the necessary properties since those are private.
What is the recommended approach for unit testing without a constructor?
This is a slimmed down version of the code.
public class Course
{
private Course()
{
}
public int Id { get; private set; }
public string Name { get; private set; }
public bool Open { get; private set; }
public virtual ICollection<Student> Students { get; private set; }
public void Register(string studentName)
{
if (Open)
{
var student = new Student(studentName);
Students.Add(student);
}
}
}
// Usage //
using (var db = new SchoolContext())
{
var course = db.Courses.Include(x => x.Students).Where(x => x.Name == courseName).First();
course.Register(studentName);
db.SaveChanges();
}
// Unit Test //
[Fact]
public void CanRegisterStudentForOpenClass(){
// HERE I HAVE NO WAY TO CHANGE THE OPEN VARIABLE
var course = (Course)Activator.CreateInstance(typeof(Course), true);
course.Register("Bob");
}

Yes you can using reflexion. your code is neraly there;
you can get properties and fields of the types with typeof(Course).GetProperty("PropertyName") then you can use SetValue to set the desired value, and pass as parameter first the instance to modify then the value.
in your case true;
note: in your example you will need to add the Collection of students too, if your Open is true.
Here there is a working example:
[Fact]
public void CanRegisterStudentForOpenClass()
{
var course = (Course)Activator.CreateInstance(typeof(Course), true);
typeof(Course).GetProperty("Open").SetValue(course, true, null);
ICollection<Student> students = new List<Student>();
typeof(Course).GetProperty("Students").SetValue(course, students, null);
course.Register("Bob");
Assert.Single(course.Students);
}

If you would rather not use reflection, then I recommend you use internal classes (instead of private) and using the InternalsVisibleToAttribute on your implementation assembly.
You can find more about the attribute here. Here's a quick guide on how you can use it!
Step 1. Add this attribute to your assembly that wants its internal code tested.
[assembly: InternalsVisibleToAttribute("MyUnitTestedProject.UnitTests")]
Step 2. Change private to internal.
public class Course
{
internal Course()
{
}
public int Id { get; internal set; }
public string Name { get; internal set; }
public bool Open { get; internal set; }
public virtual ICollection<Student> Students { get; internal set; }
/* ... */
}
Step 3. Write your tests like normal!
[Fact]
public void CanRegisterStudentForOpenClass()
{
var course = new Course();
course.Id = "#####";
course.Register("Bob");
}

As a few people have mentioned here, unit testing something private is either a code smell, or a sign you're writing the wrong tests.
In this case, what you would want to do is use EF's in-memory database if you're using Core, or mocking with EF6.
For EF6 You can follow the docs here
I would say rather than newing your dbContext where you do, pass it in via Dependency Injection. If that's beyond the scope of the work you're doing, (I'm assuming this is actual coursework, so going to DI may be overkill) then you can create a wrapper class that takes a dbcontext and use that in place.
Taking a few liberties with where this code is called from...
class Semester
{
//...skipping members etc
//if your original is like this
public RegisterCourses(Student student)
{
using (var db = new SchoolContext())
{
RegisterCourses(student, db);
}
}
//change it to this
public RegisterCourses(Student student, SchoolContext db)
{
var course = db.Courses.Include(x => x.Students).Where(x => x.Name == courseName).First();
course.Register(studentName);
db.SaveChanges();
}
}
[Fact]
public void CanRegisterStudentForOpenClass()
{
//following after https://learn.microsoft.com/en-us/ef/ef6/fundamentals/testing/mocking#testing-query-scenarios
var mockCourseSet = new Mock<DbSet<Course>>();
mockCourseSet.As<IQueryable<Course>>().Setup(m => m.Provider).Returns(data.Provider);
mockCourseSet.As<IQueryable<Course>>().Setup(m => m.Expression).Returns(data.Expression);
mockCourseSet.As<IQueryable<Course>>().Setup(m => m.ElementType).Returns(data.ElementType);
mockCourseSet.As<IQueryable<Course>>().Setup(m => m.GetEnumerator()).Returns(data.GetEnumerator());
//create an aditional mock for the Student dbset
mockStudentSet.As.........
var mockContext = new Mock<SchoolContext>();
mockContext.Setup(c => c.Courses).Returns(mockCourseSet.Object);
//same for student so we can include it
mockContext.Include(It.IsAny<string>()).Returns(mockStudentSet); //you can change the isAny here to check for Bob or such
var student = Institution.GetStudent("Bob");
var semester = Institution.GetSemester(Semester.One);
semester.RegisterCourses(student, mockContext);
}
If you're using EFCore you can follow it along from here

You can fake private constructors and members using TypeMock Isolator or JustMock (both paid) or using MS Fakes (only available in VS Enterprise).
There is also a free Pose library that allows you to fake access to properties.
Unfortunately, the private constructor can't be forged. Therefore, you will need to create an instance of the class using reflection.
Add package.
Open namespace:
using Pose;
Test code:
[Fact]
public void CanRegisterStudentForOpenClass()
{
var course = (Course)Activator.CreateInstance(typeof(Course), true);
ICollection<Student> students = new List<Student>();
Shim studentsPropShim = Shim.Replace(() => Is.A<Course>().Students)
.With((Course _) => students);
Shim openPropShim = Shim.Replace(() => Is.A<Course>().Open)
.With((Course _) => true);
int actual = 0;
PoseContext.Isolate(() =>
{
course.Register("Bob");
actual = course.Students.Count;
},
studentsPropShim, openPropShim);
Assert.Equal(1, actual);
}

You can create a JSON representation of your default instance and deserialize it with Newtonsoft.
Something like this:
using System.Reflection;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;
using privateConstructor;
namespace privateConstructorTest
{
[TestClass]
public class CourseTest
{
[TestMethod]
public void Register_WhenOpenIsTrue_EnableAddStudents()
{
// Arrange
const string json = #"{'Id': 1, 'name':'My Course', 'open':'true', 'students':[]}";
var course = CreateInstance<Course>(json);
// Act
course.Register("Bob");
// Assert
Assert.AreEqual(1, course.Students.Count);
}
[TestMethod]
public void Register_WhenOpenIsFalse_DisableAddStudents()
{
// Arrange
const string json = #"{'Id': 1, 'name':'My Course', 'open':'false', 'students':[]}";
var course = CreateInstance<Course>(json);
// Act
course.Register("Bob");
// Assert
Assert.AreEqual(0, course.Students.Count);
}
private static T CreateInstance<T>(string json) =>
JsonConvert.DeserializeObject<T>(json, new JsonSerializerSettings
{
ConstructorHandling = ConstructorHandling.AllowNonPublicDefaultConstructor,
ContractResolver = new ContractResolverWithPrivates()
});
public class ContractResolverWithPrivates : CamelCasePropertyNamesContractResolver
{
protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
{
var prop = base.CreateProperty(member, memberSerialization);
if (prop.Writable) return prop;
var property = member as PropertyInfo;
if (property == null) return prop;
var hasPrivateSetter = property.GetSetMethod(true) != null;
prop.Writable = hasPrivateSetter;
return prop;
}
}
}
}
In order to have a cleaner test class, you can extract the JSON strings and the helper code that creates the instance.

I need help mocking a method in my c# project

I'm fairly new to this TDD and I'm lost with this at the moment.
I'm trying to use .Setup to get the product by ID of 99 and check it's actually returned in .Returns(saveProduct), which causes me the error below:
enter image description here
What am I doing wrong?
public class ProductControllerTests
{
private Mock<ICart> cartMock;
private Mock<IProductRepository> productRepositoryMock;
private Mock<IOrderRepository> orderRepositoryMock;
private Mock<IProductService> productServiceMock;
private Mock<ILanguageService> languageServiceMock;
private Mock<IStringLocalizer<ProductService>> stringLocalizerMock;
private ProductViewModel product;
private ProductController productController;
public ProductControllerTests()
{
//setup
product = new ProductViewModel();
cartMock = new Mock<ICart>();
productRepositoryMock = new Mock<IProductRepository>();
orderRepositoryMock = new Mock<IOrderRepository>();
stringLocalizerMock = new Mock<IStringLocalizer<ProductService>>();
productServiceMock = new Mock<IProductService>();
languageServiceMock = new Mock<ILanguageService>();
productController = new ProductController(productServiceMock.Object, languageServiceMock.Object);
}
[Fact]
public void CreateValidModelState() // MOCKED
{
// Act
ProductService productService = new ProductService(cartMock.Object, productRepositoryMock.Object, orderRepositoryMock.Object, stringLocalizerMock.Object);
productController = new ProductController(productService, languageServiceMock.Object);
productServiceMock.Setup(x => x.SaveProduct(product)); //It works without this?!? what's it FOR!?
//Arranje
product.Id = 99;
product.Name = "Test box";
product.Description = "The best box ever.";
product.Details = "Toss it and see if it gets back.";
product.Stock = "9000";
product.Price = "9000";
var saveProduct = productController.Create(product);
//productServiceMock.Setup(x => x.GetProductById(It.IsAny<int>())).Returns(saveProduct);
//productServiceMock.SetupGet(x => x.GetProductById(99)).Returns("Test box");
//var expectedProduct = productServiceMock.GetProduct(1);
Assert.IsType<RedirectToActionResult>(saveProduct);
}
}
}

There is a lot of room for improvement in your code snippet.
First, you create private members but then you over write the variable name with local variables.
The idea behind mocking is that when you mock an interface you can Setup its' methods to return whatever you wish them to return. So in your case
productServiceMock.Setup(x => x.GetProductById(99)).Returns(saveProduct);
the line above means that wherever in your controller you have the GetProductById(int) method is called with 99 as a parameter, the method will return the saveProduct object.
You could also write the Setup like
productServiceMock.Setup(x => x.GetProductById(It.IsAny<int>())).Returns(saveProduct);
In this case wherever in your controller the GetProductById() method is called, no matter what is the parameter passed, you will get the saveProductObject.
In this test you have written I can not see any value. What I mean is that create a controller, you create the saveProduct and then you assert it is not null. Of course it is not null, because you populated above.
It would make sense to actually use one of your controllers methods that you know that the GetByUserId() method is used. Then make an assertion upon the return object based on the methods logic.
---Update---
Imagine you have a handler
public class HandlerExample {
private IInjectedService _injectedService;
public HandlerExample(IInjectedService injectedService){
_injectedService = injectedService;
}
public int Handle(testNumber)
{
var serviceResponse = _injectedService.TestMethod(testNumber);
if(serviceResponse)
return 1;
return 2;
}
}
And your interface looks like
public interface IInjectedService
{
bool TestMethod(int testNumber);
}
I won't give any example on the implementation here because it is not relevant. Your test method would then make sense to be like
[Fact]
public void Test()
{
mockedInjectedService = new Mock<IInjectedService>();
mockedInjectedService.Setup(x => x.TestMethod(99)).Returns(true);
var handler = new Handler(mockedInjectedService.Object);
var sut = handler.Handle(99);
Assert.Equal(sut, 1);
}
sut is a convention for "system under test"

How to return null when accessing a moq object?

I am using Moq library for unit testing. Now what i want is that when I access my object for the first time it should return null, and when i access this on second time it should return something else.
here is my code
var mock = new Mock<IMyClass>();
mock.Setup(?????);
mock.Setup(?????);
var actual = target.Method(mock.object);
in my method i am first checking that whether mock object is null or not, if it is null then do initialize it and then do some calls on it.
bool Method(IMyClass myObj)
{
if (myObj != null)
return true;
else
{
myObj = new MyClass();
bool result = myObj.SomeFunctionReturningBool();
return result;
}
}
what to do setup for mock object,
Also i need to know how to mock this line
bool result = myObj.SomeFunctionReturningBool();

It sounds like you are trying to run two tests with one test method - maybe it would be better to split the tests into two?
You also want to initialise a new object if the method is passed null. To test this, I suggest creating a factory object responsible for creating instances of MyClass. The new code would look like:
interface IMyClassFactory
{
IMyClass CreateMyClass();
}
bool Method(IMyClass myObj, IMyClassFactory myClassFactory)
{
if (myObj != null)
{
return true;
}
myObj = myClassFactory.CreateMyClass();
return myObj.SomeFunctionReturningBool();
}
Then the tests would look like:
[Test]
public void Method_ShouldReturnTrueIfNotPassedNull()
{
Assert.That(target.Method(new MyClass()), Is.True);
}
[Test]
public void Method_ShouldCreateObjectAndReturnResultOfSomeFunctionIfPassedNull()
{
// Arrange
bool expectedResult = false;
var mockMyClass = new Mock<IMyClass>();
mockMyClass.Setup(x => x.SomeFunctionReturningBool()).Returns(expectedResult);
var mockMyFactory = new Mock<IMyClassFactory>();
mockMyFactory.Setup(x => x.CreateMyClass()).Returns(mockMyClass.Object);
// Act
var result = target.Method(null, mockMyFactory.Object);
// Assert
mockMyClass.Verify(x => x.SomeFunctionReturningBool(), Times.Once());
mockMyFactory.Verify(x => x.CreateMyClass(), Times.Once());
Assert.That(result, Is.EqualTo(expectedResult));
}
Here the factory pattern has been used to pass in an object which can create objects of IMyClass type, and then the factory itself has been mocked.
If you do not want to change your method's signature, then create the factory in the class's constructor, and make it accessible via a public property of the class. It can then be overwritten in the test by the mock factory. This is called dependency injection.

Moq - Return null - This working example simply illustrates how to return null using Moq. While the line of code is required is the commented line below, a full working example is provided below.
// _mockShopService.Setup(x => x.GetProduct(It.IsAny<string>())).Returns(() => null);
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Moq;
public class Product
{
public string Id { get; set; }
public string Name { get; set; }
}
public interface IShopService
{
Product GetProduct(string productId);
}
public class ShopService : IShopService
{
public Product GetProduct(string productId)
{
if (string.IsNullOrWhiteSpace(productId))
{
return new Product();
}
return new Product { Id = "8160807887984", Name = "How to return null in Moq" };
}
}
public class Shop
{
private static IShopService _shopService;
public Shop(IShopService shopService)
{
_shopService = shopService;
}
public Product GetProduct(string productId)
{
Product product = _shopService.GetProduct(productId);
return product;
}
}
[TestClass]
public class ShopTests
{
Mock<IShopService> _mockShopService;
[TestInitialize]
public void Setup()
{
_mockShopService = new Mock<IShopService>();
}
[TestMethod]
public void ShopService_GetProduct_Returns_null()
{
//Arrange
Shop shop = new Shop(_mockShopService.Object);
//This is how we return null --- all other code above is to bring this line of code home
_mockShopService.Setup(x => x.GetProduct(It.IsAny<string>())).Returns(() => null);
//Act
var actual = shop.GetProduct(It.IsAny<string>());
//Assert
Assert.IsNull(actual);
}
}

To mock a result value you can do simply:
mock.Setup(foo => foo.SomeFunctionReturningBool()).Returns(true); // or false :)
for the other question, just pass null in the unit test instead of passing mock.object and your unit test cover that too. So you basically create two unit test one with:
var actual = target.Method(mock.object);
and the other one with:
var actual = target.Method(null);

Currently your SUT is tight-coupled with MyClass implementation. You can't mock objects which are instantiated with new keyword inside your SUT. Thus you cannot test your SUT in isolation, and your test is not unit test anymore. When implementation of MyClass.SomeFunctionReturningBool will change (it will return true instead of false), tests of your SUT will fail. This shouldn't happen. Thus, delegate creation to some dependency (factory) and inject that dependency to your SUT:
[Test]
public void ShouldReturnTrueWhenMyClassIsNotNull()
{
Mock<IMyClassFactory> factory = new Mock<IMyClassFactory>();
Mock<IMyClass> myClass = new Mock<IMyClass>();
var foo = new Foo(factory.Object);
Assert.True(foo.Method(myClass.Object));
}
[Test]
public void ShouldCreateNewMyClassAndReturnSomeFunctionValue()
{
bool expected = true;
Mock<IMyClass> myClass = new Mock<IMyClass>();
myClass.Setup(mc => mc.SomeFunctionReturningBool()).Returns(expected);
Mock<IMyClassFactory> factory = new Mock<IMyClassFactory>();
factory.Setup(f => f.CreateMyClass()).Returns(myClass.Object);
var foo = new Foo(factory.Object);
Assert.That(foo.Method(null), Is.EqualTo(expected));
factory.VerifyAll();
myClass.VerifyAll();
}
BTW assignment new value to method parameter does not affect reference which you passed to method.
Implementation:
public class Foo
{
private IMyClassFactory _factory;
public Foo(IMyClassFactory factory)
{
_factory = factory;
}
public bool Method(IMyClass myObj)
{
if (myObj != null)
return true;
return _factory.CreateMyClass().SomeFunctionReturningBool();
}
}

You can use TestFixture with parameter. this test will run two times and different type value.
using NUnit.Framework;
namespace Project.Tests
{
[TestFixture(1)]
[TestFixture(2)]
public class MyTest
{
private int _intType;
public MyTest(int type)
{
_intType = type;
}
[SetUp]
public void Setup()
{
if (_intType==1)
{
//Mock Return false
}
else
{
//Mock Return Value
}
}
}
}

Creating a hybrid of a mock and an anonymous object using e.g. Moq and AutoFixture?

I encountered a class during my work that looks like this:
public class MyObject
{
public int? A {get; set;}
public int? B {get; set;}
public int? C {get; set;}
public virtual int? GetSomeValue()
{
//simplified behavior:
return A ?? B ?? C;
}
}
The issue is that I have some code that accesses A, B and C and calls the GetSomeValue() method (now, I'd say this is not a good design, but sometimes my hands are tied ;-)). I want to create a mock of this object, which, at the same time, has A, B and C set to some values. So, when I use moq as such:
var m = new Mock<MyObject>() { DefaultValue = DefaultValue.Mock };
lets me setup a result on GetSomeValue() method, but all the properties are set to null (and setting up all of them using Setup() is quite cumbersome, since the real object is a nasty data object and has more properties than in above simplified example).
So on the other hand, using AutoFixture like this:
var fixture = new Fixture();
var anyMyObject = fixture.CreateAnonymous<MyObject>();
Leaves me without the ability to stup a call to GetSomeValue() method.
Is there any way to combine the two, to have anonymous values and the ability to setup call results?
Edit
Based on nemesv's answer, I derived the following utility method (hope I got it right):
public static Mock<T> AnonymousMock<T>() where T : class
{
var mock = new Mock<T>();
fixture.Customize<T>(c => c.FromFactory(() => mock.Object));
fixture.CreateAnonymous<T>();
fixture.Customizations.RemoveAt(0);
return mock;
}

This is actually possible to do with AutoFixture, but it does require a bit of tweaking. The extensibility points are all there, but I admit that in this case, the solution isn't particularly discoverable.
It becomes even harder if you want it to work with nested/complex types.
Given the MyObject class above, as well as this MyParent class:
public class MyParent
{
public MyObject Object { get; set; }
public string Text { get; set; }
}
these unit tests all pass:
public class Scenario
{
[Fact]
public void CreateMyObject()
{
var fixture = new Fixture().Customize(new MockHybridCustomization());
var actual = fixture.CreateAnonymous<MyObject>();
Assert.NotNull(actual.A);
Assert.NotNull(actual.B);
Assert.NotNull(actual.C);
}
[Fact]
public void MyObjectIsMock()
{
var fixture = new Fixture().Customize(new MockHybridCustomization());
var actual = fixture.CreateAnonymous<MyObject>();
Assert.NotNull(Mock.Get(actual));
}
[Fact]
public void CreateMyParent()
{
var fixture = new Fixture().Customize(new MockHybridCustomization());
var actual = fixture.CreateAnonymous<MyParent>();
Assert.NotNull(actual.Object);
Assert.NotNull(actual.Text);
Assert.NotNull(Mock.Get(actual.Object));
}
[Fact]
public void MyParentIsMock()
{
var fixture = new Fixture().Customize(new MockHybridCustomization());
var actual = fixture.CreateAnonymous<MyParent>();
Assert.NotNull(Mock.Get(actual));
}
}
What's in MockHybridCustomization? This:
public class MockHybridCustomization : ICustomization
{
public void Customize(IFixture fixture)
{
fixture.Customizations.Add(
new MockPostprocessor(
new MethodInvoker(
new MockConstructorQuery())));
fixture.Customizations.Add(
new Postprocessor(
new MockRelay(t =>
t == typeof(MyObject) || t == typeof(MyParent)),
new AutoExceptMoqPropertiesCommand().Execute,
new AnyTypeSpecification()));
}
}
The MockPostprocessor, MockConstructorQuery and MockRelay classes are defined in the AutoMoq extension to AutoFixture, so you'll need to add a reference to this library. However, note that it's not required to add the AutoMoqCustomization.
The AutoExceptMoqPropertiesCommand class is also custom-built for the occasion:
public class AutoExceptMoqPropertiesCommand : AutoPropertiesCommand<object>
{
public AutoExceptMoqPropertiesCommand()
: base(new NoInterceptorsSpecification())
{
}
protected override Type GetSpecimenType(object specimen)
{
return specimen.GetType();
}
private class NoInterceptorsSpecification : IRequestSpecification
{
public bool IsSatisfiedBy(object request)
{
var fi = request as FieldInfo;
if (fi != null)
{
if (fi.Name == "__interceptors")
return false;
}
return true;
}
}
}
This solution provides a general solution to the question. However, it hasn't been extensively tested, so I'd love to get feedback on it.

Probably there is a better why, but this works:
var fixture = new Fixture();
var moq = new Mock<MyObject>() { DefaultValue = DefaultValue.Mock };
moq.Setup(m => m.GetSomeValue()).Returns(3);
fixture.Customize<MyObject>(c => c.FromFactory(() => moq.Object));
var anyMyObject = fixture.CreateAnonymous<MyObject>();
Assert.AreEqual(3, anyMyObject.GetSomeValue());
Assert.IsNotNull(anyMyObject.A);
//...
Initially I tried to use fixture.Register(() => moq.Object); instead of fixture.Customize but it registers the creator function with OmitAutoProperties() so it wouldn't work for you case.

As of 3.20.0, you can use AutoConfiguredMoqCustomization. This will automatically configure all mocks so that their members' return values are generated by AutoFixture.
var fixture = new Fixture().Customize(new AutoConfiguredMoqCustomization());
var mock = fixture.Create<Mock<MyObject>>();
Assert.NotNull(mock.Object.A);
Assert.NotNull(mock.Object.B);
Assert.NotNull(mock.Object.C);

Moq: how to verify a function that takes in a object created within a method

I have the following method;
public class MyClass
{
public Repository UserRepository { get; set; }
public void CreateUser(Message someMsg)
{
if (someMsg.CanCreate)
{
var obj = new object();
UserRepository.Save(obj)
}
}
}
In my test case, I used Moq to mock out the ObjRepository and I wanted to to call verify on the "Save()" method. However, the save method takes in a object that is created within the method under test, which I cannot mock.
Is there anyway around this using Moq? I am doing this wrong?

You can have the following setup on your mock:
objRepMock.Setup(or => or.Save(It.IsAny<object>()).Callback(obj => {
// Do asserts on the object here
}

marcind got the ball rolling but I thought I'd put more code in. Your test would look like this:
var objMock = new Mock<Repository>();
objMock.Setup(x=>x.Save(It.IsAny<object>)).Verifiable();
var myclass = new MyClass{Repository = objMock.object};
var mymessage = new Mock<Message>();
myclass.CreateUser(mymessage.object);
objMock.Verify(x=>x.Save(It.IsAny<object>), Times.AtLeastOnce);

You could use dependency injection.
public Repository ObjRepository { get; set;}
public void doStuff()
{
var obj = new object();
doStuff(obj);
}
public void doStuff(Object obj)
{
ObjRepository.Save(obj)
}