2 tests to determine "public nature" of tax

There are two (2) tests that can be used to determine whether the purpose for which tax is levied and collected is "public" in nature. First is the duty test and second is the general welfare test.

[1] Duty test. Is the purpose for which the tax is levied one that the government has the duty to provide? For example, the prime duty of the Government is to serve and protect the people. Does the purpose serve the people or protect them?

[2] General welfare test. According to Article II of the Constitution, "The maintenance of peace and order, the protection of life, liberty, and property, and promotion of the general welfare are essential for the enjoyment by all the people of the blessings of democracy." Does the tax law promote the welfare of the people?