Visual Studio 2019 - cannot get a TestContext instance in test unit

Question

[admin, this is no duplicate, I haven't found the solution in other related threads, since everybody talks about older VS versions]

I try to get a TestContext in my test unit in VS2019

no matter what I get a NULL reference

I used the code from the doc

internal class SomeClass: IDisposable
{
    private TestContext testContextInstance;
    /// <summary>
    ///Gets or sets the test context which provides
    ///information about and functionality for the current test run.
    ///</summary>
    public TestContext TestContext
    {
        get
        {
            return testContextInstance;
        }
        set
        {
            testContextInstance = value;
        }
    }
...

so what am I missing ? thanks for your help