Understanding the MSTest TestContext

问题:

Using MSTest, I needed to obtain the name of the current test from within the [TestInitialize] method. You can get this from the TestContext.TestName property.

I found an unexpected difference in behaviour between a static TestContext that is passed in to the [ClassInitialize] method and one that is declared as a public property (and gets set by the test runner).

Consider the following code:

using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace TestContext.Tests
{
    [TestClass]
    public class UnitTest1
    {
        public TestContext TestContext { get; set; }

        private static TestContext _testContext;

        [ClassInitialize]
        public static void SetupTests(TestContext testContext)
        {
            _testContext = testContext;
        }

        [TestInitialize]
        public void SetupTest()
        {
            Console.WriteLine(
                "TextContext.TestName='{0}'  static _testContext.TestName='{1}'",
                TestContext.TestName,
                _testContext.TestName);
        }

        [TestMethod] public void TestMethod1() { Assert.IsTrue(true); }

        [TestMethod] public void TestMethod2() { Assert.IsTrue(true); }

        [TestMethod] public void TestMethod3() { Assert.IsTrue(true); }
    }
}

This causes the following to be output (copy-pasted from the Resharper test runner output in VS2013):

TextContext.TestName='TestMethod1'  static _testContext.TestName='TestMethod1'
TextContext.TestName='TestMethod2'  static _testContext.TestName='TestMethod1'
TextContext.TestName='TestMethod3'  static _testContext.TestName='TestMethod1'

I had previously assumed that the two instances of TestContext would be equivalent, but clearly they're not.

• The public TestContext property behaves as I expect
• The private static TestContext value that gets passed to the [ClassInitialize] method does not. Since TestContext has properties that relate to the currently running test, this implementation seems misleading and broken

Is there any scenario where you would actually prefer to use the TestContext passed to the [ClassInitialize] method, or it is best ignored and never used?

回答1:

As [ClassInitialize] is only called at the beginning, the test name is TestMethod1. This is stale after the first test run.

TestContext is set for every method, and thus has the current test name.

Yes, it is a bit silly.

回答2:

The method

[ClassInitialize]
public static void SetupTests(TestContext testContext) { }

is called before the property set TestContext is set. So if you need the context in SetupTests then the parameter is usefull. Otherwise use the TestContext property, which is set before each

[TestInitialize]
public void SetupTest() { }

回答3:

Scenario: context for each test.

Applies to Visual Studio 2017 with the following libraries:

• Microsoft.VisualStudio.TestPlatform.TestFramework
• Microsoft.VisualStudio.TestPlatform.TestFramework.Extensions

Sample code:

    [TestClass]
    public class MyTestClass
    {

        public TestContext TestContext { get; set; }

        /// <summary>
        /// Run before each UnitTest to provide additional contextual information.
        /// TestContext reinitialized before each test, no need to clean up after each test.
        /// </summary>
        [TestInitialize]
        public void SetupTest()
        {
            TestContext.Properties.Add("MyKey", "My value ...");

            switch (TestContext.TestName)
            {
                case "MyTestMethod2":
                    TestContext.Properties["MyKey2"] = "My value 2 ...";
                    break;
            }

        }

        [TestMethod]
        public void MyTestMethod()
        {
            // Usage:
            // TestContext.Properties["MyKey"].ToString()
        }   

        [TestMethod]
        public void MyTestMethod2()
        {
            // Usage:
            // TestContext.Properties["MyKey"].ToString()

            // also has:
            // TestContext.Properties["MyKey2"].ToString()
        }

    }