Testing Strategies

Overview

Learn testing strategies for value objects. Covers unit test patterns, test helpers, and architecture tests.

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Learning Objectives

• Value object creation test patterns
• Equality test patterns
• Comparability test patterns
• Using Fin<T> test helpers

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How to Run

cd Docs/tutorials/Functional-ValueObject/04-practical-guide/04-Testing-Strategies/TestingStrategies
dotnet run

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Expected Output

=== Value Object Testing Strategies ===

1. Creation Test Patterns
────────────────────────────────────────
   [Valid input test] user@example.com -> PASS
   [Invalid input test] invalid-email -> PASS
   [Error message verification] Contains '@' -> PASS
   [Boundary value test] Empty string/null -> PASS

2. Equality Test Patterns
────────────────────────────────────────
   [Same value equality] email1 == email2 -> PASS
   [Different value inequality] email1 != email3 -> PASS
   [Hash code consistency] hash(email1) == hash(email2) -> PASS
   [Operator test] == and != -> PASS

3. Comparability Test Patterns
────────────────────────────────────────
   [CompareTo test] 20 < 25 < 30 -> PASS
   [Comparison operator test] < operator -> PASS
   [Sorting test] Order after sorting -> PASS

4. Test Helper Usage
────────────────────────────────────────
   [ShouldBeSuccess helper] -> PASS
   [ShouldBeFail helper] -> PASS
   [GetSuccessValue helper] -> PASS
   [GetFailError helper] -> PASS

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Core Code Explanation

1. Fin Test Helpers

public static class FinTestExtensions
{
    public static void ShouldBeSuccess<T>(this Fin<T> fin)
    {
        if (fin.IsFail)
        {
            var message = fin.Match(_ => "", e => e.Message);
            throw new Exception($"Expected Succ but got Fail: {message}");
        }
    }

    public static void ShouldBeFail<T>(this Fin<T> fin)
    {
        if (fin.IsSucc)
            throw new Exception("Expected Fail but got Succ");
    }

    public static T GetSuccessValue<T>(this Fin<T> fin) => ...;
    public static Error GetFailError<T>(this Fin<T> fin) => ...;
}

2. Test Pattern Examples

// Creation test
[Fact]
public void Create_WithValidEmail_ShouldSucceed()
{
    var result = Email.Create("user@example.com");

    result.ShouldBeSuccess();
    var email = result.GetSuccessValue();
    ((string)email).ShouldBe("user@example.com");
}

// Equality test
[Fact]
public void Equals_WithSameValue_ShouldBeTrue()
{
    var email1 = Email.CreateFromValidated("user@example.com");
    var email2 = Email.CreateFromValidated("user@example.com");

    email1.ShouldBe(email2);
    email1.GetHashCode().ShouldBe(email2.GetHashCode());
}

// Comparison test
[Fact]
public void Sort_ShouldOrderByValue()
{
    var ages = new[] { Age.CreateFromValidated(30), Age.CreateFromValidated(10) };

    Array.Sort(ages);

    ages[0].Value.ShouldBe(10);
    ages[1].Value.ShouldBe(30);
}

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Test Checklist

Creation Tests

• Valid input -> success
• Invalid input -> failure
• Boundary value tests (empty string, null, min/max values)
• Error message verification

Equality Tests

• Same values -> equal
• Different values -> not equal
• Hash code consistency
• == / != operators

Comparison Tests (when applicable)

• CompareTo accuracy
• <, >, <=, >= operators
• Sorting behavior

Immutability Tests

• Original unchanged after operations

FAQ

Q1: Why are Fin<T> test helpers needed?

A: Directly verifying the success/failure of Fin<T> requires calling Match and checking conditions repeatedly. Using helpers like ShouldBeSuccess() and ShouldBeFail() makes test code concise, and error messages are clearly output on failure.

Q2: Why are boundary value tests important for value objects?

A: The Create method of a value object is the last line of defense for validation. If validation is not confirmed to work correctly for boundary conditions like empty strings, null, min/max values, invalid values may enter the system.

Q3: Must hash code consistency also be verified in equality tests?

A: Yes. C#‘s Dictionary and HashSet use GetHashCode() to manage keys. If two equal objects have different hash codes, the collection will not work correctly, so when Equals is true, hash codes must also be equal.

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Next Steps

Learn practical domain examples in Part 5.

-> 5.1 E-commerce Domain