CODEWITHSUNDEEP
vb.netmockingmstest
RamNow
RamNow

Reputation: 486

MSTest: How to mock a dependet object?

I'm new to unit tests, so please forgive me if this is a noob-question:

I'm trying to test a function:

<TestMethod>
Public Sub CheckSomethingTest()
        Dim testObject as new MyClass()
        Assert.IsTrue(testObject.CheckSomething(), "Check failed")
End Sub

The MyClass.CheckSomething function is accessing a global shared method which is making a database-query.

Public Function CheckSomething() as Boolean
    Dim length as Integer = GlobalModule.GetLegthFromDb()
    Return length > 0
End Function

Content of GlobalModule:

Public Class GlobalModule

    Public Shared Function GetLegthFromDb() As Integer
        'pretend database is not available
        Throw New InstanceNotFoundException("DB Connetion not set")
    End Function
End Class

As the database is not available for the test, I get a Nullpointer exception.

Is there any way to mock (or something else) the GetLegthFromDb method for the test?

Upvotes: 0

Views: 2654

Answers (2)

RamNow
RamNow

Reputation: 486

After some additional research I found a solution that fits my requirements:

I used Microsoft Fakes for mocking the Shared Function.

<TestMethod>
Public Sub CheckSomethingTest()
    Using s = Microsoft.QualityTools.Testing.Fakes.ShimsContext.Create()
        MockTest.Fakes.ShimGlobalModule.GetLegthFromDb = Function() As Integer
                                                             Return 111
                                                         End Function

        Dim testObject As New MyClassA
        Assert.IsTrue(testObject.CheckSomething(), "Check failed")
    End Using
End Sub

MockTest is the Namespace of my project.

Upvotes: 0

AD.Net
AD.Net

Reputation: 13399

GlobalModule needs to be injectable in the class and when you instantiate the class you're trying to test, you can inject a mock of GlobalModule in that class. It's also better to have it interfaced.

The code is in C# since it's easier for me, but you probably can translate it easily. 

public class MyClass()
{
  IGlobalModule _globalModule;
  public MyClass (IGlobalModule globalModule)
  {
     _globalModule = globalModule; // use this in the method
  }
  public bool CheckSomething()
  {
     return _globalModule.GetLegthFromDb() > 0;
  }
}

For the test:

var mock = new Mock<IGlobalModule>();
mock.SetUp(m=>m.GetLegthFromDb()).Returns(100);//whatever you want to return    
var testObject = new MyClass(mock.Object);

Assert.IsTrue(testObject.CheckSomething(), "Check failed")

Upvotes: 1

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