Testing fundamentals

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Testing Fundamentals Deep Dive

Overview

Testing strategy should maximize confidence per minute of execution and maintenance cost.

Core Concepts

• Fast, deterministic tests close to business logic.
• Fewer but meaningful integration tests.
• Selective UI and end-to-end tests for critical journeys.

Test Pyramid and Strategy

• Unit tests: broad coverage, low runtime cost.
• Integration tests: boundary correctness.
• UI/E2E tests: user-critical flows only.

Tooling and Infrastructure

• JUnit + coroutine test APIs.
• MockWebServer for network determinism.
• CI sharding for parallel execution.

Flaky Test Mitigation

• Eliminate timing assumptions.
• Replace real clocks and dispatchers.
• Isolate shared mutable test state.

Code Examples

@Test
fun repository_returnsCachedValueBeforeNetwork() {
    // Arrange
    // Act
    // Assert
}

Common Interview Questions

• Q: How do you pick the right test layer? A: Answer by test pyramid intent: unit for logic speed, integration for boundaries, and end-to-end for critical journeys with flakiness controls.
• Q: What makes a suite trustworthy? A: Answer by test pyramid intent: unit for logic speed, integration for boundaries, and end-to-end for critical journeys with flakiness controls.
• Q: How do you reduce flaky runs? A: Answer by test pyramid intent: unit for logic speed, integration for boundaries, and end-to-end for critical journeys with flakiness controls.

Production Considerations

• Test failures should be actionable.
• Keep test runtime budgets for CI.

Performance Insights

• Prioritize test parallelism and hermetic setup.

Senior-Level Insights

• Strong strategy balances speed, reliability, and maintainability.