The Fourth Phase of Testing: Why Chaos Engineering Belongs in Your CI Pipeline

                      Phase 1: Unit Tests
  └── Tests a single unit of logic in isolation
  └── Fast, precise, tells you the code is correct
  └── Cannot tell you the system handles failure

Phase 2: Integration Tests
  └── Tests interactions between components
  └── Catches interface mismatches and contract violations
  └── Still uses predictable, cooperative dependencies

Phase 3: Container Tests (Testcontainers, Docker Compose)
  └── Runs real databases, brokers, caches
  └── Validates real-system behavior with real dependencies
  └── Dependencies are healthy, well-behaved, and available

Phase 4: Chaos Tests   ← the missing phase
  └── Injects controlled failures into real system components
  └── Validates recovery logic, circuit breakers, retry strategies
  └── Proves your system handles the unexpected, not just the expected
                    

                      # /tmp/.chaos-net.conf — 10% connection failures to your downstream
tcp4://payments-service:8080:connect:ECONNREFUSED:0.10

# /tmp/.chaos-dns.conf — transient DNS failures for internal services
dns://*.internal:EAI_AGAIN:0.15

# Inject faults into any process — no code changes
LD_PRELOAD=libchaos-net.so:libchaos-dns.so ./your-service
                    

                      @SpringBootTest
@ChaosTest
class PaymentServiceChaosTest {

    @Test
    void circuitBreaker_opens_on_jdbcPoolExhaustion(ChaosSession session) {
        try (var h = session.activate(
                ChaosScenario.jdbc()
                    .reject("chaos: pool exhausted")
                    .probability(1.0)
                    .maxApplications(3)
                    .build())) {

            try (var scope = session.bind()) {
                // First 3 JDBC borrows fail → circuit must open
                assertThat(service.charge(order))
                    .isEqualTo(PaymentResult.REJECTED_CIRCUIT_OPEN);
            }
        }
    }
}
                    

                      @Testcontainers
@ExtendWith(ChaosTestingExtension.class)
@SyscallLevelChaos(LibchaosLib.NET)
class OrderServiceChaosTest {

    @Container @AppContainer
    static GenericContainer<?> app =
        new GenericContainer<>("order-service:latest")
            .withExposedPorts(8080);

    @Test
    @IncidentChaosK8sRollingUpdateRst(toxicity = 0.3)
    void service_handles_rst_during_rolling_deploy() {
        // 30% of RECV calls return ECONNRESET — exactly what happens
        // during a Kubernetes rolling update when iptables lags behind
        assertThat(callService("/api/order/42")).isEqualTo(200);
    }
}