Article 6 of the US Constitution states that no "religious test" can be required for any office or public trust.
The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution; but no religious test shall ever be required as a qualification to any office or public trust under the United States.
What exactly is a "religious test" in this context? Is it adherence to a religion (e.g. "you must/must not be Protestant")? Is it having a religious belief (e.g. "you must/must not have religious grounds for abortion immoral")? Or something else?
To give a concrete example, this article claims that Democratic senators are creating a religious test by indicating that they are not wanting to approve a judicial nomination who is a member of the Knights of Columbus (a Catholic volunteer organization that is pro-life). Assuming that this an accurate assessment of their motivation, would that count as a religious test?