public class CalculatorTest {

    private readonly ITestOutputHelper _outputHelper;

    public CalculatorTest(ITestOutputHelper outputHelper) {
        _outputHelper = outputHelper;

        _outputHelper.WriteLine("An output in constructor");
    }

    [Fact]
    public void Given_When_Then() {
        ...
        _outputHelper.WriteLine("An output in a test");
        ...
    }
}