CODEWITHSUNDEEP
c#.netunit-testingmockingnsubstitute
mbadawi23
mbadawi23

Reputation: 1071

NSubstitute: Mock method is not returning expected result

I'm new to NSubstitute, mocking, and unit testing in general.

I'm trying to use NSubstitute to remove some dependencies I have in my class under test, but methods in the mock objects are not behaving as I expect based on how I configured them. Here is an example I created in Visual Studio:

  1. Interface and concrete class to be substituted. Notice, MyConcreteClass.MyMethod() returns false:

    public interface IMyInterface
{
    bool MyMethod(string arg);
}

public class MyConcreteClass : IMyInterface
{
    public bool MyMethod(string arg)
    {
        return false;
    }
}

  2. My class under test:

    public class MyTestedClass
{
    private IMyInterface _concrete;

    public MyTestedClass()
    {
        _concrete = new MyConcreteClass();
    }

    public MyTestedClass(IMyInterface mock)
    {
        _concrete = mock;
    }

    public bool MyConcreteMethod(string arg)
    {
        return _concrete.MyMethod(arg);
    }
}

  3. My unit test class for MyTestedClass:

    [TestClass]
public class UnitTest1
{
    [TestMethod]
    public void Given_MyMethodIsUsingAMock_ShouldReturnTrue()
    {
        // Arrange
        var myMock = Substitute.For<IMyInterface>();
        myMock.MyMethod("blah").Returns(true);
        var myTestedObject = new MyTestedClass(myMock);

        // Act
        var result = myTestedObject.MyConcreteMethod("blah blah");

        // Assert
        Assert.AreEqual(result, true); // This assertion fails!
    }

    [TestMethod]
    public void Given_MyMethodIsNotMock_ShouldReturnFalse()
    {
        // Arrange
        var myTestedObject = new MyTestedClass();

        // Act
        var result = myTestedObject.MyConcreteMethod("blah blah");

        // Assert
        Assert.AreEqual(result, false); // This assertion passes.
    }
}

  4. Test results show that Given_MyMethodIsUsingAMock_ShouldReturnTrue() fails:

    MyUnitTests (2 tests) [0:00.190] Failed: 1 test failed
 MyUnitTests (2 tests) [0:00.190] Failed: 1 test failed
  UnitTest1 (2 tests) [0:00.190] Failed: 1 test failed
   Given_MyMethodIsNotMock_ShouldReturnFalse [0:00.000] Success
   Given_MyMethodIsUsingAMock_ShouldReturnTrue [0:00.189] Failed
Assert.AreEqual failed. Expected:<False>. Actual:<True>. 
   at MyUnitTests.UnitTest1.Given_MyMethodIsUsingAMock_ShouldReturnTrue() in "c:\MyWorkspace\projects\NSubstituteMocking\MyUnitTests\UnitTest1.cs":line 23

It looks like I'm missing a trivial configuration, but it is eluding me.

Upvotes: 2

Views: 5160

Answers (1)

Nkosi
Nkosi

Reputation: 247098

The MyMethod is arranged to return true when given "blah" 

myMock.MyMethod("blah").Returns(true);

but is then provide it with "blah blah" when being acted upon. 

var result = myTestedObject.MyConcreteMethod("blah blah");

As the expected/arranged parameter did not match, the mock did not behave as configured.

Provide the mock with what it expects to receive for it to behave as expected.

[TestMethod]
public void Given_Blah_MyConcreteMethod_ShouldReturnTrue() {
    // Arrange
    var myMock = Substitute.For<IMyInterface>();
    var arg = "blah";
    var expected = true;
    myMock.MyMethod(arg).Returns(expected);
    var myTestedObject = new MyTestedClass(myMock);

    // Act
    var actual = myTestedObject.MyConcreteMethod(arg);

    // Assert
    Assert.AreEqual(expected, actual); // This should pass
}

Note the use of variables to store the provided and expected values so that mistakes can be reduced when exercising the test.

Upvotes: 5

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