Testing Strategies Exercises

Testing Strategies - Practice Exercises

A comprehensive set of exercises covering unit, integration, and system testing.

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Foundations

Exercise 1: AAA Structure

Q: Rewrite a test to use Arrange-Act-Assert.

A: Separate setup, execution, and assertions with clear sections.

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Exercise 2: Pure Function Unit Test

Q: Write a unit test for a method that calculates fees.

A: Provide inputs, call the method, and assert the exact output.

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Exercise 3: Mocking a Repository

Q: Mock a repository to return a fixed entity.

A:

_repo.Setup(r => r.GetByIdAsync(id)).ReturnsAsync(entity);

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Exercise 4: Exception Assertions

Q: Assert that a handler throws BadRequestException.

A:

await Should.ThrowAsync<BadRequestException>(() => handler.Handle(cmd, ct));

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Exercise 5: Parameterized Tests

Q: Use [Theory] with [InlineData] to test multiple inputs.

A: Parameterized tests reduce duplication and improve coverage.

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Exercise 6: Test Naming

Q: Use the Method_Scenario_Expected naming pattern.

A: Example: Handle_InvalidCommand_ThrowsBadRequest.

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Exercise 7: Test Data Builders

Q: Create a builder for a complex Order entity.

A: Builders keep tests focused and avoid repeated setup.

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Exercise 8: Test Isolation

Q: Ensure tests do not depend on shared static state.

A: Reset shared data between tests or use fresh fixtures per test.

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Exercise 9: Stub vs Mock

Q: Explain when to use a stub vs a mock.

A: Use stubs for data, mocks for verifying interactions.

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Exercise 10: Assertions with Shouldly

Q: Convert Assert.Equal to Shouldly syntax.

A:

result.ShouldBe(expected);

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Exercise 11: Edge Case Coverage

Q: Add tests for null inputs and empty collections.

A: Validate defensive behavior and error handling paths.

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Exercise 12: Avoid Over-Mocking

Q: Why is over-mocking risky?

A: It couples tests to implementation details and can miss integration issues.

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Integration

Exercise 13: Testcontainers for Databases

Q: Spin up a temporary SQL container for integration tests.

A: Use Testcontainers to start a database per test run.

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Exercise 14: WebApplicationFactory

Q: Use WebApplicationFactory for API tests.

A: Create a client and call endpoints in memory.

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Exercise 15: Middleware Tests

Q: Test an exception-handling middleware.

A: Use a test server and verify the response status and body.

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Exercise 16: Contract Tests for HTTP Clients

Q: Validate assumptions about a downstream API.

A: Use Pact or similar tools to enforce contracts.

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Exercise 17: Consumer-Driven Contracts

Q: Explain how CDC reduces integration failures.

A: Consumers specify expectations, providers verify them in CI.

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Exercise 18: SQLite In-Memory EF Core

Q: Use SQLite in-memory for EF Core integration tests.

A: It supports relational behavior better than the InMemory provider.

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Exercise 19: Transaction Rollback

Q: Roll back DB changes after each test.

A: Use a transaction scope and rollback in teardown.

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Exercise 20: Background Service Integration Test

Q: Test a hosted service end-to-end.

A: Start the host and observe side effects or emitted events.

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Exercise 21: Message Handler Testing

Q: Test a message handler with an in-memory bus.

A: Publish a message and assert state changes or produced events.

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Exercise 22: Retry Policy Verification

Q: Verify a retry policy is applied to HTTP calls.

A: Use a fake HTTP handler and assert call count.

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Exercise 23: Snapshot Testing

Q: When is snapshot testing useful?

A: For stable outputs like API docs or structured responses.

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Exercise 24: Integration Test Cleanup

Q: Ensure tests clean up queues or caches.

A: Use teardown hooks to clear state and avoid test bleed.

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Advanced

Exercise 25: TDD Cycle

Q: Describe the Red-Green-Refactor cycle.

A: Write a failing test, make it pass, then refactor safely.

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Exercise 26: Property-Based Testing

Q: Use property-based testing to validate invariants.

A: Generate many inputs and assert a property always holds.

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Exercise 27: Mutation Testing

Q: What does mutation testing reveal?

A: It identifies weak tests that do not fail when code is mutated.

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Exercise 28: Idempotency Tests

Q: Ensure a command is safe to retry.

A: Run the same command twice and assert no duplicate side effects.

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Exercise 29: Concurrency Tests

Q: Test a handler under parallel execution.

A: Use Parallel.ForEachAsync and assert thread-safe outcomes.

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Exercise 30: Timeout and Cancellation

Q: Verify cancellation tokens are honored.

A: Pass a canceled token and assert early exit.

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Exercise 31: Fake Clock

Q: Test time-dependent logic without real delays.

A: Inject IClock and control time in tests.

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Exercise 32: Cache Behavior

Q: Ensure cache hits avoid repository calls.

A: Use a mock repository and verify Get is not called on cache hit.

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Exercise 33: Logging Assertions

Q: Assert warning logs on invalid input.

A: Capture logs with a test logger and assert message templates.

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Exercise 34: Allocation Tests

Q: Detect allocations in a hot path.

A: Use BenchmarkDotNet or dotnet-counters to confirm zero allocations.

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Exercise 35: Resilience Under Failure

Q: Simulate partial dependency failures.

A: Stub downstream calls to fail and assert graceful degradation.

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Scenarios

Exercise 36: Order Placement Integration

Q: Test a full order placement flow.

A: Call the API, verify DB state, and ensure events are emitted.

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Exercise 37: Market Data Ingestion

Q: Validate a pipeline processes messages in order.

A: Publish ordered messages and assert output ordering.

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Exercise 38: API Versioning Test

Q: Ensure v1 and v2 endpoints both work.

A: Call both versions and verify compatible responses.

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Exercise 39: Auth and Role Tests

Q: Test role-based access to endpoints.

A: Use a test auth handler and verify 403 for unauthorized roles.

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Exercise 40: Smoke Test Checklist

Q: Define a smoke test for deployment.

A: Health checks, basic CRUD, and a latency budget assertion.