Mocking Method with out-param

[Christian]

class and method

public class A
{
  public static bool TryGet<T>(string key, out T obj)
  {
      ....
  }
}

 
usage

public static object AMethod(string key)
{
object values;

if (A.TryGet(key, out values))
{
  return values;
}

return null;
}

now i want to write a test for method AMethod and mock A.TryGet. How can I do that? I tried different approaches, but wasnt able to create a mock of the TryGet extension. I want to set the "obj" variable in the "TryGet" method do different values depending on the passed key (using "Returns" or "DoInstead")

[Kaloyan]

Hello Christian,

Thank you for contacting our forums.

I wrote the following test method and it behaves as expected:

[TestMethod]
public void AMethod_OnExecuteWithAnyStringAndArrangedPositiveBool_ShouldReturnAsExpected()
{
    object expected = "test";

    // Arrange - When A.TryGet<object>() is called with any string argument,
    //  it should return true and pass the value of "expected" to the out argument.
    Mock.Arrange(() => A.TryGet<object>(Arg.AnyString, out expected)).Returns(true);

    // Act
    object actualOutArg = string.Empty;
    var actual = AMethod("any string here");

    // Assert
    Assert.AreEqual(expected, actual);
}

The only thing you should be careful with is matching the constraints and the arguments in the arrangement.

For example, if you have another method (similar to the AMethod, but a string function), like this:

public static string StringMethod(string key)
{
    string values;

    if (A.TryGet(key, out values))
    {
        return values;
    }

    return null;
}

You will need to pass out string as an argument in the arrangement and also arrange for  A.TryGet<string>() as follows:

string expectedString = "test1";

// Arrange - When A.TryGet<string>() is called with any string argument,
//  it should return true and pass tha value of "expected" to the out argument.
Mock.Arrange(() => A.TryGet<string>(Arg.AnyString, out expectedString)).Returns(true);

// Act
object actualOutArg = string.Empty;
var actual = StringMethod("any string here");

// Assert
Assert.AreEqual(expectedString, actual);

I hope this helps. Please, let me know if there is anything else I can assist you with.

Regards,
Kaloyan
Telerik

[Christian]

thank you. I think that would work in my case. However how would you set up the mock if you have something like:

public static object AMethod(string key)
{
Hashtable values = new Hashtable();

if (A.TryGet(key, out values))
{
 values.Add("A", "abc");
}

return values;
}

Now i want to write a test for method "AMethod" that tests if the returned Hashtable contains the value "abc"?

[TestMethod]

public void AMethod_OnExecuteWithAnyStringAndArrangedPositiveBool_ShouldReturnAsExpected()

{

    Hashtableexpected = new Hashtable();
  expected.Add("A", "abc");

 

    // setup mock here


    //?? Mock.Arrange(() => A.TryGet<object>(Arg.AnyString, out expected)).Returns(true);

 

    // Act

    Hashtable actual = AMethod("any string here");

 

    // Assert

    Assert.AreEqual(expected, actual);

}

[Kaloyan]

Hi again Christian,

I am glad my previous answer helped you.

About your next question, I made this example:

// You will pass this Hashtable as an out-param in the arrangement.
// Then you will assert against it, as it should be populated according to the method being tested.
Hashtable actual = new Hashtable();

// Arrange - This time we use Hashtable as a constraint.
Mock.Arrange(() => A.TryGet<Hashtable>(Arg.AnyString, out actual)).Returns(true);

// Act
AMethod("any string here");

// Assert - We assert against our expectations.
Assert.AreEqual(1, actual.Count);
Assert.IsTrue(actual.ContainsKey("A"));
Assert.IsTrue(actual.ContainsValue("abc"));

Note that, you don`t need to populate the Hashtable inside the test method. As the method under test (AMethod) is supposed to do this, we should only assert against our expectations.

Let me know if this works for you.

Regards,
Kaloyan
Telerik