codeql/csharp/ql/test/library-tests/dataflow/fields/C_ctor.cs

public class C_no_ctor
{
    private Elem s1 = Util.Source<Elem>(1);

    void M1()
    {
        C_no_ctor c = new C_no_ctor();
        c.M2();
    }

    public void M2()
    {
        Util.Sink(s1); // $ hasValueFlow=1
    }
}

public class C_with_ctor
{
    private Elem s1 = Util.Source<Elem>(1);

    void M1()
    {
        C_with_ctor c = new C_with_ctor();
        c.M2();
    }

    public C_with_ctor() { }

    public void M2()
    {
        Util.Sink(s1); // $ hasValueFlow=1
    }
}

class Util
{
    public static void Sink(object o) { }

    public static T Source<T>(object source) => throw null;
}

public class Elem { }