ExpectedExceptionBaseAttribute Class

Article
04/28/2015

This is a base class for attributes that specify to expect an exception from a unit test.

Inheritance Hierarchy

Object
  Attribute
    Microsoft.VisualStudio.TestTools.UnitTesting.ExpectedExceptionBaseAttribute
      Microsoft.VisualStudio.TestTools.UnitTesting.ExpectedExceptionAttribute

Namespace: Microsoft.VisualStudio.TestTools.UnitTesting
Assembly: Microsoft.VisualStudio.QualityTools.UnitTestFramework (in Microsoft.VisualStudio.QualityTools.UnitTestFramework.dll)

Syntax

'Declaration
<AttributeUsageAttribute(AttributeTargets.Method, AllowMultiple := False, Inherited := True)> _
Public MustInherit Class ExpectedExceptionBaseAttribute _
    Inherits Attribute

[AttributeUsageAttribute(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
public abstract class ExpectedExceptionBaseAttribute : Attribute

[AttributeUsageAttribute(AttributeTargets::Method, AllowMultiple = false, Inherited = true)]
public ref class ExpectedExceptionBaseAttribute abstract : public Attribute

[<AbstractClass>]
[<AttributeUsageAttribute(AttributeTargets.Method, AllowMultiple = false, Inherited = true)>]
type ExpectedExceptionBaseAttribute =  
    class 
        inherit Attribute 
    end

public abstract class ExpectedExceptionBaseAttribute extends Attribute

The ExpectedExceptionBaseAttribute type exposes the following members.

Constructors

	Name	Description
	ExpectedExceptionBaseAttribute()	Initializes a new instance of the ExpectedExceptionBaseAttribute class.
	ExpectedExceptionBaseAttribute(String)	Initializes a new instance of the ExpectedExceptionBaseAttribute class.

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Properties

	Name	Description
	NoExceptionMessage	Infrastructure.
	TestContext	Infrastructure.
	TypeId	When implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)

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Methods

	Name	Description
	Equals	Infrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Returns the hash code for this instance. (Inherited from Attribute.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	IsDefaultAttribute	When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
	Match	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	RethrowIfAssertException	Throws the exception again if it is an AssertFailedException or an AssertInconclusiveException.
	ToString	Returns a string that represents the current object. (Inherited from Object.)
	Verify	Infrastructure.

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Explicit Interface Implementations

	Name	Description
	System#Runtime#InteropServices#_Attribute#GetIDsOfNames	Maps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
	System#Runtime#InteropServices#_Attribute#GetTypeInfo	Retrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
	System#Runtime#InteropServices#_Attribute#GetTypeInfoCount	Retrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
	System#Runtime#InteropServices#_Attribute#Invoke	Provides access to properties and methods exposed by an object. (Inherited from Attribute.)

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Remarks

By implementing your own expected exception verification. you can specify additional information and requirements that the built-in methods of the ExpectedExceptionAttribute class cannot handle, such as the following:

Verifying the state of the exception.
Expecting more than one type of exception.
Displaying a custom message when a wrong type of exception is thrown.
Controlling the outcome of a negative test.
For more information about how to use attributes, see Extending Metadata Using Attributes.

Examples

The following class contains the method to test.

using System;

namespace CSExample
{
    public class DivisionClass
    {
        private int fraction;

        public int Divide(int numerator, int denominator)
        {
            return numerator / denominator;
        }
    }
}

The following custom attribute class, ExpectedArithmeticException, derives from the ExpectedExceptionBaseAttribute class to verify an exception type and message. The ExpectedArithmeticException attribute verifies that a test method throws an exception of a type that is or derives from System.ArithmeticException. It also verifies that the exception message matches the specified exception message. The unit test will pass because it throws a DivideByZeroException, which derives from ArithmeticException, and the specified exception message matches the message of the exception that is thrown by the unit test.

using CSExample;
using Microsoft.VisualStudio.TestTools.UnitTesting;
namespace TestProject1
{
    public sealed class ExpectedArithmeticException : ExpectedExceptionBaseAttribute
    {
        private string exceptionMessage;
        private string wrongExceptionMessage;

        public string WrongExceptionMessage
        {
            get
            {
                return wrongExceptionMessage;
            }
            set
            {
                wrongExceptionMessage = value;
            }
        }

        public ExpectedArithmeticException(string expectedExceptionMessage) : this(expectedExceptionMessage, "No exception was thrown.")
        {
        }

        public ExpectedArithmeticException(string expectedExceptionMessage, string noExceptionMessage)
            : base(noExceptionMessage)
        {
            exceptionMessage = expectedExceptionMessage;
            WrongExceptionMessage = "The exception that was thrown does not derive from System.ArithmeticException.";
        }

        protected override void Verify(System.Exception exception)
        {
            Assert.IsNotNull(exception);

            // Handle assertion exceptions from assertion failures in the test method, since we are not interested in verifying those
            base.RethrowIfAssertException(exception);

            Assert.IsInstanceOfType(exception, typeof(System.ArithmeticException), wrongExceptionMessage);
            Assert.AreEqual(exceptionMessage, exception.Message, "Could not verify the exception message.");
        }
    }


    [TestClass()]
    public class DivisionClassTest
    {

        /* This test will pass because it thows a System.DivideByZeroException which derives from System.ArithmeticException. */
        [TestMethod()]
        [ExpectedArithmeticException("Attempted to divide by zero.", "An exception was expected, but no exception was thrown.", WrongExceptionMessage = "The wrong type of exception was thrown.")]
        public void DivideTest()
        {
            DivisionClass target = new DivisionClass();
            int numerator = 5;
            int denominator = 0;
            int actual;
            actual = target.Divide(numerator, denominator);
        }

    }
}

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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