Sub Main

    Dim specs = Enumerable.Range(0, 3).ToArray
    Dim tests = Enumerable.Range(0, 5).ToArray

    Dim TestSpecs = (From s In specs _
                     From t In tests _
                     Select New SpecimenTest With {.SpecimenID = S, .TestID = t}).ToArray

    TestSpecs.Dump

    Dim ByTestID = TestSpecs.GroupBy(Function(t) t.TestID)

    ByTestID.Dump("ByTestID")

End Sub

' Define other methods and classes here
Class SpecimenTest
        Public SpecimenID As Integer
        Public TestID As Integer
End Class