Use unit testing to ensure code quality and catch bugs early. Unit testing is a software testing technique that involves testing individual units or components of a software application in isolation from the rest of the system. In .NET Core and C#, unit testing is typically done using a testing framework such as NUnit or xUnit. Unit tests are automated, repeatable, and can be run quickly, making them an effective way to catch bugs early in the development process and ensure code quality.

Unit testing is useful for several reasons. First, it helps to catch bugs early in the development process, before they become more difficult and expensive to fix. By testing individual units of code in isolation, developers can identify and fix issues before they are integrated into the larger system. Second, unit testing helps to ensure code quality by providing a way to test individual units of code against expected results. This can help to catch issues such as logic errors, boundary cases, and performance problems. Finally, unit testing can help to improve code maintainability by providing a way to test code changes and ensure that they do not introduce new bugs or regressions.

Here is an example of a simple unit test in C# using NUnit:

[TestFixture]
public class MyTestClass
{
    [Test]
    public void MyTestMethod()
    {
        // Arrange
        int a = 1;
        int b = 2;
        int expected = 3;

        // Act
        int result = MyMathClass.Add(a, b);

        // Assert
        Assert.AreEqual(expected, result);
    }
}

public class MyMathClass
{
    public static int Add(int a, int b)
    {
        return a + b;
    }
}

In this example, we have a simple test that checks the behavior of the Add method in the MyMathClass class. The test sets up some initial values for the input parameters and the expected result, then calls the Add method and compares the result to the expected value using the Assert.AreEqual method. If the result does not match the expected value, the test will fail and indicate that there is a problem with the code.