C#: How do you implement unit testing?

1public class CalculatorTests
2{
3    [Fact]
4    public void Add_ReturnsSum()
5    {
6        var calc = new Calculator();
7        Assert.Equal(5, calc.Add(2, 3));
8    }
9
10    [Theory]
11    [InlineData(2, 3, 5)]
12    [InlineData(0, 0, 0)]
13    public void Add_ReturnsSum_Parameterized(int a, int b, int expected)
14    {
15        var calc = new Calculator();
16        Assert.Equal(expected, calc.Add(a, b));
17    }
18}

1var mock = new Mock<IUserService>();
2mock.Setup(s => s.GetByIdAsync(1))
3    .ReturnsAsync(new User { Name = "Alice" });