C# Testing with MSTest In-Depth

MSTest — Test Framework

• [TestMethod] — a test with no parameters

  [TestClass]
  public class CalculatorTests
  {
      [TestMethod]
      public void Add_TwoPositiveNumbers_ReturnsSum()
      {
          // Arrange
          var calculator = new Calculator();
  
          // Act
          int result = calculator.Add(3, 4);
  
          // Assert
          Assert.AreEqual(7, result);
      }
  }
  

• [DataTestMethod] + [DataRow] — parameterized tests

  [TestClass]
  public class CalculatorTests
  {
      [DataTestMethod]
      [DataRow(1, 2, 3)]
      [DataRow(0, 0, 0)]
      [DataRow(-1, 1, 0)]
      [DataRow(int.MaxValue, 0, int.MaxValue)]
      public void Add_VariousInputs_ReturnsExpectedSum(int a, int b, int expected)
      {
          var calculator = new Calculator();
          int result = calculator.Add(a, b);
          Assert.AreEqual(expected, result);
      }
  }
  

• [DynamicData] — complex or external test data

  public static IEnumerable<object[]> DiscountTestData =>
      new List<object[]>
      {
          new object[] { new Customer { OrderCount = 0, IsActive = true }, 0.00m },
          new object[] { new Customer { OrderCount = 5, IsActive = true }, 0.05m },
          new object[] { new Customer { OrderCount = 15, IsActive = true }, 0.15m },
          new object[] { new Customer { OrderCount = 15, IsActive = false }, 0.00m },
      };
  
  [TestClass]
  public class DiscountCalculatorTests
  {
      [DataTestMethod]
      [DynamicData(nameof(DiscountTestData), DynamicDataSourceType.Property)]
      public void GetDiscount_VariousCustomers_ReturnsExpectedRate(Customer customer, decimal expectedDiscount)
      {
          var calculator = new DiscountCalculator();
          decimal discount = calculator.GetDiscount(customer);
          Assert.AreEqual(expectedDiscount, discount);
      }
  }
  

• [TestCategory] — organize tests by category

  [TestClass]
  public class EmailValidatorTests
  {
      [DataTestMethod]
      [DataRow("user@example.com", true)]
      [DataRow("user@sub.domain.com", true)]
      [DataRow("invalid", false)]
      [DataRow("@no-local.com", false)]
      [DataRow("", false)]
      [TestCategory("Validation")]
      public void IsValidEmail_VariousInputs_ReturnsExpected(string email, bool expected)
      {
          bool result = EmailValidator.IsValid(email);
          Assert.AreEqual(expected, result);
      }
  }
  

MSTest Best Practices

• Always decorate test classes with [TestClass].
• Use [TestInitialize] and [TestCleanup] for setup/teardown logic.
• Prefer [DataTestMethod] and [DataRow] for parameterized tests.
• Use [ExpectedException] for exception testing.
• Organize tests with [TestCategory] for filtering.

References:

• Microsoft Docs: MSTest