To determine the smallest number of tests required to ascertain if the sceptervirus is currently present or has been present in the city, let's analyze the given conditions for the test results:

1. Virus positive: Indicates there is at least one currently infected individual among the tested samples, and none of them have antibodies from previous infections.

2. Antibody positive: Indicates there is at least one individual healed from a previous infection among the samples, with no currently infected individuals.

3. Neutral: This result implies that either all individuals tested are not infected, or there is a mix of currently infected persons and previously infected (and now healed) individuals, thus neutralizing each other's presence.

### Objective

We need to strategically design the testing process to determine if there is a current infection or if there has been a previous infection, using the smallest number of tests.

### Solution Approach

To achieve this, consider the following:

- Each citizen falls into one of three categories: currently infected, previously infected (healed), or naive (neither infected nor healed).

- A single test can give us sufficient information about the presence of a virus or antibodies among the selected group.

- By testing each citizen individually, we can directly determine the category to which each citizen belongs—specifically, whether they are currently infected or have antibodies from a previous infection.

### Testing Strategy

Given that we have $n$ citizens, the simplest strategy to achieve our objective is:

- Test each citizen individually.

This approach ensures that:
- If any test comes back virus-positive, we know that the virus is currently present.
- If any test comes back antibody-positive, we know that the virus was present previously.

By applying a separate test to each individual, we guarantee the detection of any current or past virus presence without ambiguity. Therefore, the minimum number of tests required is:

$$\boxed{n}$$

This solution is both straightforward and optimal as each individual test provides definitive information about each citizen's current or past infection status, collectively revealing the city's overall virus presence.