1, this test should pass (per the "return empty array when n == 0" rule):
Assert.AreEqual(new double[] { }, Tribonacci(new double[] { 1, 5, 7 }, 0));

2, tests like this should be removed:
Assert.AreEqual(new double[] { 300 }, Tribonacci(new double[] { 300, 5, 7 }, 0));
Assert.AreEqual(new double[] { 0 }, Tribonacci(new double[] { 8, 5, 7 }, 0));

Can you fix the kata, then?

This issue still isn't solved. I had to return an array of length 1 instead of an empty array when n == 0.

Done

An empty array in C# is achieved with e.g. "new int[0]".
If you can't change the testing suite you should change the description to something like "if n==0, then return an array of length 1, containing only a 0".

I know little to nothing of that language: as I mentioned earlier, if anyone wants to pass me the right info, I might attempt to add them to the template code, as we can no longer change the testing suite for that version.

C#

Language?

The kata is wrong. In Instruction is stated "if n==0, then return an empty array", but your basic test requires it to be an array with one element: number zero. This is very frustrating, please corret the test.