How to restrict test data method call for respective Test method by using TestCaseSource attribute in NUnit

Question

I am using NUnit for the Selenium C# project. In which I have many test methods. For getting data (from excel) I am using a public static method that returns IEnumerable<TestCaseData> which I am calling at test method level as TestCaseSource. I am facing challenges now, as I start executing on the test method it is invoking all the static methods which are there in the project.

Code looks like this:

    public static IEnumerable<TestCaseData> BasicSearch()
        {
            BaseEntity.TestDataPath = PMTestConstants.PMTestDataFolder + ConfigurationManager.AppSettings.Get("Environment").ToString() + PMTestConstants.PMTestDataBook;
            return ExcelTestDataHelper.ReadFromExcel(BaseEntity.TestDataPath, ExcelQueryCreator.GetCommand(PMTestConstants.QueryCommand, PMTestConstants.PMPolicySheet, "999580"));
        }


        [Test, TestCaseSource("BasicSearch"), Category("Smoke")]
        public void SampleCase(Dictionary<string, string> data)
        {
            dosomething;         
        } 

Can someone help me how can I restrict my data call method to the respective test method?

Answer 1

Your TestCaseSource is not actually called by the test method when you run it, but as part of test discovery. While it's possible to select a single test to execute, it's not possible to discover tests selectively. NUnit must examine the assembly and find all the tests before it's possible to run any of them.

To make matters worse, if you are running under Visual Studio, the discovery process takes place multiple times, first before the tests are initially displayed and then again each time the tests are run. This is made necessary by the architecture of the VS Test Window, which runs separate processes for the initial disovery and the execution of the tests.

That makes it particularly important to minimize the amount of work done in test discovery, especially when running under Visual Studio. Ideally, you should structure the code so that the variable parameters are recorded during discovery. The actual data access should take place at execution time. This can be done in a OneTimeSetUp method, a SetUp method or at the start of the test itself.

Finally, I'd say that your instinct is correct: it should be possible to set up a TestCaseSource, which only runs if the test you select is about to be executed. Unfortunately, that's a feature that NUnit doesn't yet have.