
# C# Testing with MSTest In-Depth

---

## MSTest — Test Framework

- **[TestMethod] — a test with no parameters**

  ```csharp
  [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**

  ```csharp
  [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**

  ```csharp
  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**

  ```csharp
  [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](https://learn.microsoft.com/en-us/dotnet/core/testing/unit-testing-with-mstest)


Learn MSTest fundamentals, attributes, and patterns for robust unit testing in C# applications. Includes practical examples and best practices.

MSTest

C# Testing with MSTest In-Depth

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