AssemblyInitializeAttribute Class

Identifies a method that contains code to be used before all tests in the assembly have run and to allocate resources obtained by the assembly. This class cannot be inherited.

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


<AttributeUsageAttribute(AttributeTargets.Method, AllowMultiple := False)> _
Public NotInheritable Class AssemblyInitializeAttribute _
    Inherits Attribute
Dim instance As AssemblyInitializeAttribute
[AttributeUsageAttribute(AttributeTargets.Method, AllowMultiple = false)]
public sealed class AssemblyInitializeAttribute : Attribute
[AttributeUsageAttribute(AttributeTargets::Method, AllowMultiple = false)]
public ref class AssemblyInitializeAttribute sealed : public Attribute
public final class AssemblyInitializeAttribute extends Attribute


The method marked with this attribute will be run before methods marked with the ClassInitializeAttribute, TestInitializeAttribute, and TestMethodAttribute attributes. Only one method in an assembly may be decorated with this attribute.

Important noteImportant Note:

This attribute should not be used on ASP.NET unit tests, that is, any test with [HostType("ASP.NET")] attribute. Because of the stateless nature of IIS and ASP.NET, a method decorated with this attribute might be called more than once per test run.

This attribute can be specified on a method. Only one instance of this attribute may be applied to a method.


The test engine runs a method that is marked with the AssemblyInitialize attribute only if that method is a member of a class that is marked with the TestClass attribute.

For more information about how to use attributes, see Extending Metadata Using Attributes.


The following examples demonstrate the initialization and clean-up attributes that are used to indicate which methods should be run by the test engine at different periods of the test.

The first code samples contain a class and method to test. To run this example, create a class library project and replace the code with the following example.

using System;

namespace SampleClassLib
    public class DivideClass
        public static int DivideMethod(int denominator)
            return (2 / denominator);
Imports System

Namespace SampleClassLib
    Public Class DivideClass
        Shared Function DivideMethod(ByVal denominator As Integer) As Integer
            Return 2 \ denominator
        End Function
    End Class
End Namespace

The following example contains code to test DivideMethod() found in the previous code examples. Create a test project and put the following code in a test class document. Add the appropriate references to the project. This code contains attributes that control the initialization and clean-up execution order for the method, class, and assembly.

In particular, note the AssemblyInitialize attribute on the AssemblyInit()method.

using Microsoft.VisualStudio.TestTools.UnitTesting;
using SampleClassLib;
using System;
using System.Windows.Forms;

namespace TestNamespace
    public sealed class DivideClassTest
        public static void AssemblyInit(TestContext context)
            MessageBox.Show("AssemblyInit " + context.TestName);

        public static void ClassInit(TestContext context)
            MessageBox.Show("ClassInit " + context.TestName);

        public void Initialize()

        public void Cleanup()

        public static void ClassCleanup()

        public static void AssemblyCleanup()

        public void DivideMethodTest()
Imports Microsoft.VisualStudio.TestTools.UnitTesting
Imports SampleClassLib2.SampleClassLib
Imports System
Imports System.IO
Imports System.Windows.Forms

Namespace TestNamespace
    <TestClass()> _
    Public NotInheritable Class DivideClassTest
        <AssemblyInitialize()> _
        Public Shared Sub AssemblyInit(ByVal context As TestContext)
            MsgBox("AssemblyInit " + context.TestName)
        End Sub 'AssemblyInit

        <ClassInitialize()> _
        Public Shared Sub ClassInit(ByVal context As TestContext)
            MsgBox("ClassInit " + context.TestName)
        End Sub 'ClassInit

        <TestInitialize()> _
        Public Sub Initialize()
        End Sub 

        <TestCleanup()> _
        Public Sub Cleanup()
        End Sub 

        <ClassCleanup()> _
        Public Shared Sub ClassCleanup()
        End Sub 

        <AssemblyCleanup()> _
        Public Shared Sub AssemblyCleanup()
        End Sub

        <TestMethod()> _
        <ExpectedException(GetType(System.DivideByZeroException))> _
        Public Sub DivideMethodTest()
        End Sub
    End Class
End Namespace

Inheritance Hierarchy


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.

See Also


AssemblyInitializeAttribute Members

Microsoft.VisualStudio.TestTools.UnitTesting Namespace

Other Resources

Anatomy of a Unit Test

Unit Testing Framework