Property Tests

Note

The property accessor being tested will prefix the test method identifier. For example, if you are testing the set accessor of a property, the test identifier would begin Set.

Example 1 - Set Accessor Throws Exception

Test Case:

#	Test Case	Test Data	Expected
1	Exception when the value is a negative value	Value: -1	ArgumentOutOfRangeException, Parameter: value, Message: The value must be zero or greater., State is not updated.

Testing Goal: Set the property to an invalid value.

C#

[TestMethod]
public void SetAmountOfMoney_ToValueLessThanZero_ThrowsException()
{
    // Arrange
    string name = "Kenny";
    decimal amountOfMoney = 100;

    Person person = new Person(name, amountOfMoney);

    // Act & Assert
    ArgumentOutOfRangeException exception = Assert.ThrowsException<ArgumentOutOfRangeException>(() => person.AmountOfMoney = -1);

    // Assert exception state
    Assert.AreEqual("value", exception.ParamName);
    Assert.AreEqual("The value must be zero or greater.", GetExceptionMessage(exception.Message));

    // Reflection
    PrivateObject target = new PrivateObject(person);

    // Obtain object state
    decimal actual = (decimal)target.GetField("amountOfMoney");

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

Notes:

• The Assert.ThrowsException() method is used since an exception is expected to occur and the state of the exception is verified.
• In most cases, when an exception is thrown in a set accessor, the state should not change to the invalid value. The final Assert statement verifies this.

Example 2 - Set Accessor Valid Value

Test Case:

#	Test Case	Test Data	Expected
3	Sets the amount of money to zero	Initial amount of money: 100, Value: 0	0

Testing Goal: Sets the property to a valid value and verifies the state changed.

C#

[TestMethod]
public void SetAmountOfMoney_ToZero_StateUpdated()
{
    // Arrange
    string name = "Kenny";
    decimal amountOfMoney = 100;

    Person person = new Person(name, amountOfMoney);

    decimal expected = 0;

    // Act
    person.AmountOfMoney = expected;

    // Reflection
    PrivateObject target = new PrivateObject(person);

    // Obtain object state
    decimal actual = (decimal)target.GetField("amountOfMoney");

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

Notes:

• When testing a modification in state, the value you choose to change the state should be different than the initial value.
• The variable expected is a recommended practice as it makes the Assert statement clearer.
• Due to the result of the unit changing the state, accessing the private field is required to verify the test.

Example 3 - Get Accessor

Test Case:

#	Test Case	Test Data	Expected
4	Gets the amount of money	Initial amount of money: 100	100

Testing Goal: Initialize the object and obtain its state.

C#

[TestMethod]
public void GetAmountOfMoney_ReturnsState()
{
    // Arrange
    string name = "Kenny";
    decimal amountOfMoney = 100;

    Person person = new Person(name, amountOfMoney);

    // Act
    decimal actual = person.AmountOfMoney;

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

Notes:

• The test method identifier does not require the scenario part.
• PrivateObject should not be used in this test as no private member is accessed.

Auto-Implemented Property Tests

When a property is auto-implemented, it will not have a field you can access. When you are in this situation, you will use the GetProperty() method of the PrivateObject class.

C#

public abstract class Shape
{
    public double XCoordinate { get; set; }
}

public class Circle : Shape
{

}

C#

[TestMethod]
public void SetXCoordinate_ToNewCoordinate_StateUpdated()
{
    // Arrange
    string color = "Black";
    double radius = 77.7;
    double xCoordinate = 123.4;

    Circle circle = new Circle(color, radius);

    // Act
    circle.XCoordinate = xCoordinate;

    PrivateObject target;
    target = new PrivateObject(circle);

    double actual = (double)target.GetProperty("XCoordinate");

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