Why are some of my Unit Tests being run multiple times?

Question

When I run all of the Unit Tests in my solution using Visual Studio's built-in testing engine, I'll see that some tests are run multiple times, while others are only run once:

Test Result Window

It appears that if there are multiple TestClass es in the same file, things get confusing. In this file, for example:

[TestClass]
public class AerationEngineTests
{
    protected IAerationEngine aerationEngine;
    protected AerationPackage aerationPackage;
    protected BinPackage bin;

    [TestInitialize]
    public void TestInitialize()
    {
        aerationEngine = new AerationEngine();
        aerationPackage = new AerationPackage();
        bin = new BinPackage();
        bin.Children.Add(new Shell {ShellDiameter = 75, RingCount = 15, RingHeight = RingHeights.RingHeight32});
    }

    [TestMethod]
    public void ShouldCalculateFloorArea()
    {
        // Arrange


        // Act
        var floorArea = aerationEngine.CalculateFloorArea(aerationPackage, bin);

        // Assert
        floorArea.ShouldBeInRange(4417.86, 4417.87);
    }

    [TestMethod]
    public void ShouldCalculateBinCapacity()
    {
        // Arrange
        aerationPackage.FillType = FillTypes.Peaked;
        var grainDepth = aerationEngine.CalculateGrainDepth(aerationPackage, bin);
        var floorArea = aerationEngine.CalculateFloorArea(aerationPackage, bin);
        var calculations = new FanCalculations {GrainDepth = grainDepth, FloorArea = floorArea};

        // Act
        var binCapacity = aerationEngine.CalculateMaxBinCapacity(calculations);

        // Assert
        binCapacity.ShouldBeInRange(175525.88, 175525.9);
    }

    [TestMethod]
    public void ShouldCalculateTargetAirFlow()
    {
        // Arrange
        aerationPackage.FillType = FillTypes.Peaked;
        aerationPackage.DesiredAirFlow = AirFlowRates.AirFlowOne4th;
        var grainDepth = aerationEngine.CalculateGrainDepth(aerationPackage, bin);
        var floorArea = aerationEngine.CalculateFloorArea(aerationPackage, bin);
        var calculations = new FanCalculations {GrainDepth = grainDepth, FloorArea = floorArea};
        var binCapacity = aerationEngine.CalculateMaxBinCapacity(calculations);
        calculations.MaxBinCapacity = binCapacity;

        // Act
        var airflow = aerationEngine.CalculateTargetAirflow(aerationPackage, calculations);

        // Assert
        airflow.ShouldBeInRange(43881.46, 43881.48);
    }

    [TestMethod]
    public void ShouldCalculateTargetAirFlowPerFan()
    {
        // Arrange
        aerationPackage.FillType = FillTypes.Peaked;
        aerationPackage.DesiredAirFlow = AirFlowRates.AirFlowOne4th;
        aerationPackage.FanCount = 4;
        var grainDepth = aerationEngine.CalculateGrainDepth(aerationPackage, bin);
        var floorArea = aerationEngine.CalculateFloorArea(aerationPackage, bin);
        var calculations = new FanCalculations {GrainDepth = grainDepth, FloorArea = floorArea};
        var binCapacity = aerationEngine.CalculateMaxBinCapacity(calculations);
        calculations.MaxBinCapacity = binCapacity;
        var airflow = aerationEngine.CalculateTargetAirflow(aerationPackage, calculations);
        calculations.TargetAirFlow = airflow;
        // Act
        var flowPerFan = aerationEngine.CalculateTargetAirflowPerFan(aerationPackage, calculations);

        // Assert
        flowPerFan.ShouldBeInRange(10970.3, 10970.4);
    }

    [TestMethod]
    public void ShouldCalculateFloorPressure()
    {
        // Arrange

        // Act
        var floorPressure = aerationEngine.CalculateFloorPressure(aerationPackage, bin);

        // Assert
        floorPressure.ShouldBeInRange(1943.0, 1945.0);
    }

    [TestMethod]
    public void ShouldCalculateTrenchWidth()
    {
        // Arrange
        aerationPackage.FillType = FillTypes.Peaked;
        aerationPackage.DesiredAirFlow = AirFlowRates.AirFlowOne4th;
        aerationPackage.FanCount = 4;
        var grainDepth = aerationEngine.CalculateGrainDepth(aerationPackage, bin);
        var floorArea = aerationEngine.CalculateFloorArea(aerationPackage, bin);
        var calculations = new FanCalculations {GrainDepth = grainDepth, FloorArea = floorArea};
        var binCapacity = aerationEngine.CalculateMaxBinCapacity(calculations);
        calculations.MaxBinCapacity = binCapacity;
        var airflow = aerationEngine.CalculateTargetAirflow(aerationPackage, calculations);
        calculations.TargetAirFlow = airflow;
        var flowPerFan = aerationEngine.CalculateTargetAirflowPerFan(aerationPackage, calculations);
        calculations.TargetAirFlowPerFan = flowPerFan;

        // Act
        var trenchWidth = aerationEngine.CalculateTrenchWidth(calculations);

        // Assert
        trenchWidth.ShouldBe(72);
    }
}

[TestClass]
public class CalculateGrainDepthMethod : AerationEngineTests
{
    [TestInitialize]
    public new void TestInitialize()
    {
        base.TestInitialize();
    }

    [TestMethod]
    public void ShouldCalculateLevelFillHeight()
    {
        // Arrange
        aerationPackage.FillType = FillTypes.Level;

        // Act
        var grainDepth = aerationEngine.CalculateGrainDepth(aerationPackage, bin);

        // Assert
        grainDepth.ShouldBe(40.0);
    }

    [TestMethod]
    public void ShouldCalculatePeakedFillHeight()
    {
        // Arrange
        aerationPackage.FillType = FillTypes.Peaked;

        // Act
        var grainDepth = aerationEngine.CalculateGrainDepth(aerationPackage, bin);

        // Assert
        grainDepth.ShouldBeInRange(46.64, 46.66);
    }
}

The tests inside of CalculateGrainDepthMethod get run once, but the rest of the test methods get run twice, and they're grouped under CalculateGrainDepthMethod . See this pic (using ReSharper's tools):

ReSharper Test result window

It doesn't appear that there are two testing engines running at the same time, but maybe there are? Or maybe I just structured the tests themselves incorrectly? Does anyone know why these tests would run more than once, and why they'd be grouped under classes to which they don't belong?

Answer 1

You are inheriting class CalculateGrainDepthMethod inherits from AerationEngineTests . Because of this tests in class AerationEngineTests are executing twice.

[TestClass]
public class CalculateGrainDepthMethod : AerationEngineTests
{

Either have the dependencies contained in class CalculateGrainDepthMethod or create a test helper which initializes these values and use it in both your test classes.