NUnit: How to pass TestCaseData from a non-static method?

Question

My test fails because of the message:

The sourceName specified on a TestCaseSourceAttribute must refer to a static field, property or method.

This is my Code:

const double MAX_DELTA = 0.01;
Qv_ges qv_ges_NE;
double Sum_Qv_ges_R_FL;
Qv_ges Qv_ges_Quer;

[SetUp]
public void init()
{
    qv_ges_NE = Din1946.Calc_Qv_ges_NE(205.7d);
    Sum_Qv_ges_R_FL = 15d + 15d + 15d + 15d + 15d + 10d + 10d + 10d + 10d + 10d + 10d + 10d;
    Qv_ges_Quer = Din1946.Calc_Qv_ges_Quer(qv_ges_NE, Sum_Qv_ges_R_FL);
}

public IEnumerable<TestCaseData> TestCases_A()
{
    yield return new TestCaseData(72.5, Qv_ges_Quer.FL.Value, MAX_DELTA);
    yield return new TestCaseData(169.17, Qv_ges_Quer.RL.Value, MAX_DELTA);
    yield return new TestCaseData(241.67, Qv_ges_Quer.NL.Value, MAX_DELTA);
    yield return new TestCaseData(314.17, Qv_ges_Quer.IL.Value, MAX_DELTA);
}

[TestCaseSource("TestCases_A")]
public void MethodA(double expected, double value, double latitude)
{
    Assert.AreEqual(expected, value, latitude);
}

I used only static testcase-methods, but now I need to access non staic data like the variable Qv_ges_Quer: Qv_ges_Quer.IL.Value, Qv_ges_Quer.FL.Value.... so I removed static

Question:
How can I use a non static testcase?
I also noticed by debugging that it doesn't enter the SetUp at first.

This is my old code which I want to reorganize, maybe you know another/better way then the way above:

public void MethodA()
{
    Qv_ges qv_ges_NE = Din1946.Calc_Qv_ges_NE(205.7d);

    double Sum_Qv_ges_R_FL = 15d + 15d + 15d + 15d + 15d + 10d + 10d + 10d + 10d + 10d + 10d + 10d;
    Qv_ges Qv_ges_Quer = Din1946.Calc_Qv_ges_Quer(qv_ges_NE, Sum_Qv_ges_R_FL);

    Assert.AreEqual(72.5, Qv_ges_Quer.FL.Value, MAX_DELTA);
    Assert.AreEqual(169.17, Qv_ges_Quer.RL.Value, MAX_DELTA);
    Assert.AreEqual(241.67, Qv_ges_Quer.NL.Value, MAX_DELTA);
    Assert.AreEqual(314.17, Qv_ges_Quer.IL.Value, MAX_DELTA);
}

Answer 1

By design, the method, property or field used by the TestCaseSourceAttribute must be static. This is intended to avoid the need to instantiate the fixture class at the time the tests are loaded. Your fixture is only instantiated when we start the run - in the case of the GUI, each time we start the run - and its lifetime is only as long as it takes to run the fixture.

In your case, you have appear to have discovered that you can use a static method. That's best, if possible.

The only way to use instance methods here is to use the constructor TestCaseSourceAttribute(Type sourceType) where sourceType implements IEnumerable and returns your test case data directly. If you use this, I recommend using a different class from your TestFixture. It's not absolutely necessary. If you use the same class, different instances will be created at load time and run time, which have no connection whatsoever with one another. Many developers end up getting confused by this and try to leave state behind at load time for use by the tests. That won't work.