Testing strategies for modern software architectures are evolving. As we transition from monolithic structures to team-sized microservices with crisp APIs aligned to bounded contexts, we encounter more stable testing surfaces. This shift leads many high-performing teams to favor integration tests over fine-grained, brittle unit tests. These integration tests, which are closer to the functional requirements, prove more trustworthy and are more resilient to internal refactoring, though they may come with a higher cost. In a vivid and engaging style, this talk addresses the primary challenges of integration testing in the microservices era: cognitive overload, test isolation, and test execution speed. Join the testing revolution and discover how to enhance your team's testing efficiency and effectiveness.

1. 1 © VictorRentea.ro
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Tes$ng Microservices
Join the Revolu-on !
at
victorrentea@gmail.com VictorRentea.ro @victorrentea

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👋 Hi, I'm Victor Rentea 🇷🇴 PhD(CS): VictorRentea.ro
Java Champion, 18 years of code, 10 years of teaching
Consultant & Trainer for 120+ companies:
❤ Clean Code, Architecture, Unit Tes3ng
🛠 Spring, Hibernate, Reac3ve/WebFlux
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https://martinfowler.com/articles/practical-test-pyramid.html
E2E
Tes$ng Pyramid
Test a thin slice of behavior
Test a group of modules
Test everything as whole
⭐ Deep Edge Case
⭐ Cri4cal Business Flow (eg. checkout)
overlapping is expected
surface is propor9onal to quan9ty

4. 5 https://martinfowler.com/articles/practical-test-pyramid.html
End-to-end
The Tes&ng Pyramid
For Monoliths

5. 6
§The Legacy Monolith
can hide huge complexity behind a few entry points
è Tes8ng deep corners only possible with Unit Tests
§Microservices
have more APIs = stable test surfaces
hide less code complexity, but more configura8on risk
è Write more Integra-on Tests è
For Monoliths

6. 7
Integra-on
(one microservice)
Integrated
(en-re ecosystem)
Deploy all microservices in dockers / staging env
Expensive, slow, fragile tests
Use for cri8cal business flows (eg checkout)
Cover one microservice fully
Use for every flow ⭐⭐⭐
Isolate tests without mocks
Cover 1 class/role (Solitary/Social Unit Testsè)
Use for naturally isolated pieces with high complexity.
@Mock are allowed
Honeycomb Tes,ng Strategy
Testcontainers 🐳
WireMock
&co
Contract
Tests
(Pact, SCC)
DB ES Kafka ...
API
many tests on
one entry point
h$ps://engineering.atspo2fy.com/2018/01/tes2ng-of-microservices/
Implementa>on
Detail
(a role)
complexity
decouple and
test in isola4on

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Unit Tests verify narrow a slice of behavior,
decoupled from dependencies (using Mocks),
without star8ng up the applica8on.
What bugs can slip past Unit Tests?
(lock, tap, doors, umbrella)
- Actual behavior of A does not match the mock(A)
- Bad @Query seman8c
- Framework magic fails to work:
@Transac8onal, @Cacheable, @Secured, @EventListener
- Misconfigured Library: Rabbit, Resilience4j, ...
- The response from an API call is not what you expected
....

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Integra,on Tests
give us more confidence that our code will really work in Produc8on,
by also covering:
ü The real stuff, without mocks
ü Correct library configura8on
ü Magic features of frameworks
ü Closer aligned to func8onal requirements

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Integra,on Tes,ng Challenges
🔗 Test Coupling
💥 Flaky Tests
🐢 Slow Tests
🧠 Cogni:ve Load
💰 Investment in CI, libs, training

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Add a Bit of Code

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🔗 Test Coupling

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You run your test suite
Test #13 is RED
To debug it, you run that test alone:
... and test #13 turns GREEN: 😱
??!!!?!
Test Coupling

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You run your test suite
All GREEN
You add your test
Another later test turns RED❌
(untouched!)
??!!!?!
??!!!?!
Test Coupling #2

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Test Coupling
Accidental: data forgo>en in ...
§DB
§Queues è drain
§Cache è clear
§State of singletons è reset
IntenConal: Stateful user journey
§Chained calls to mulCple endpoints

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Cleanup DB
§Manual Delete
- @BeforeEach & @AfterEach void cleanup() {repo.deleteAll();}
§SQL Script
- @Sql(script="classpath:cleanup.sql", phase=BEFORE_TEST_METHOD)
§@Transac4onal on Test Class
- Start each @Test in its own transacCon that is rolled back at the end
- Simplest, but: fails if tested code runs in a different transacCon, and can miss bugs*
§Reboot Spring to recreate in-memory DB/MQ/Mongo...
- @DirtiesContext
§Custom Extension
- eg Truncate all tables you find in DB- link
* h3ps://dev.to/henrykeys/don-t-use-transac>onal-in-tests-40eb

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ads 10..60 seconds to test -me è
Spring
Longer Build!
DO NOT PUT IT ON CI
Find other ways!
@DirtiesContext

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If every test leaves the DB empty
you can expect to find nothing in DB
What if we won't expect this?
🤔

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Test Data Slices
§Uniquely idenCfy our test data
- Don't assume we start on an empty DB
§Examples:
- repo.save(new Supplier()).getId(): supplierId; use it to create a Product
- API: Create Product: productId; Place Order { productId }
- r=uuid(); insert user {name=r}; select * from user where name=r and ...
- Such tests could run in parallel 😬

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§Dedicated Physical DB (like 00s)
§In-memory DB
- eg: H2 emula8ng SQL syntax via Compa8bility MODE=Oracle (eg)
✅ Simple setup
§Prod-like DB in a Docker 🐳
- eg: postgres:11-my-corp-tweaks spined of by tests via Testcontainers.org
✅ Can run incremental scripts (liquibase, flyway, ...)
✅ Can use DB-specific SQL: CONNECT BY, CONVERT(name, 'US7ASCII'), PL/SQL
What DB to use in Tests?

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💥 Flaky Tests

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- The build is failed. It's that test again!
- IDN, It worked on my machine™! Run it again!
(20 minutes later)
- What?! It passed this Cme!
- Told ya!😏
What to do about it?
> Make it reliable, then put it back on CI
⚠ "Tests o)en fail" aVtude is unhealthy

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CI Retaliates
haps://www.youtube.com/watch?v=1EGk2rvZe8A

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§Calls systems out of your control 😱
§TesCng work happening in another thread:
- MQ Listeners
- Mul8-threaded: @Async, CompletableFuture.runAsync()
§ Hack: inject a synchronous executor: link
- @Scheduled(rate=/cron=)
§ Consider: disable scheduler + call the method
Flaky? Possible Causes:

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§Block test:
- Mockito.verify(mock, timeout(1000)).call();
- Blocking message receive
§Callback-based à block the test thread using
- Latch
- CompletableFuture.complete(result)
§Poll for the effect: (how are your clients gonna do it?)
- Awaitility.await().atMost(5, SECONDS)
.pollInterval(50, MILLISECONDS)
.untilAsserted(() -> loanRepo.find(id).status == APPROVED);
Tes$ng Async Work

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🐢 Slow Tests

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Build Failed!
😖

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Build Failed!

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👍
All tests should complete
in <10..12 minutes
Build Failed!

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Each banner during tests means += 10..50s build Cme
Spring can Start Slow

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Spring can Start Slow
The same Spring context is reused
by different test classes

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§Spring Context is reused across test classes sharing the same:
- @MockBeans
- @Ac+veProfiles
- Proper+es: @TestPropertySource,..
- and others...
§Debug:
- logging.level.org.springframework.test.context.cache=DEBUG (SO answer) and see in log:
- Spring test ApplicaConContext cache staCsCcs: [size = 7, hitCount = 1780, missCount = 7, ...]
§Mul9ple app instances are started at the same 9me⚠
- ⚠ Risk = @Scheduled, Compe8ng message listeners
Spring Context Cache
Reduce number of
unique combina8ons

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Speeding up Spring Boot Tests
1. Faster VM startup: -ea -noverify -XX:TieredStopAtLevel=1 and grant more memory -mx4G
3. Slice Tests – Don't start unused parts of Spring, eg @DataJpaTest, @WebMvcTest...
h3ps://spring.io/blog/2016/08/30/custom-test-slice-with-spring-boot-1-4 and h3ps://stackoverflow.com/a/49663075
5. Run Tests on Mul>ple Threads - DANGEROUS😱
2. Reuse expensive resources across Test Classes
Ø Spring Context (previous slide)
Ø Testcontainers Dockers 🐳 (SO)
Ø WireMock/MockServer instances
Ø Profile execu>on of your tests è
4. Run fast tests at commit, defer slow tests: @Tag("slow") or ...IT suffix
Run load tests, UI robots, batches, ... only 1-2/day, eg using Maven surefire plugin (at every push) vs failsafe (nightly)

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Running Tests on Mul$ple Threads

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Running Tests on Mul$ple Threads
§Can see impressive decrease in Cme (up to - 70%)
☢ Risk: tests race on
- Files, sta8c variables
- @MockBean when/verify 😱
- DB/MQ è use @Transac8onal or test-data-slices
è Run unsafe test class with @Execu8on(SAME_THREAD)
h3ps://www.baeldung.com/junit-5-parallel-tests

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🧠 Cogni4ve Load

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Deep Tests

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Deep Tests Require Tools
§Private helper func:ons to simplify your @Tests
§Object Mother
- Tweak 'standard' test values for your need
§Tes:ng DSL (framework)
- Example: h@ps://github.com/sandromancuso/cleancoders_openchat/blob/openchat-unclebob/src/test-
integra9on/java/integra9on/IT_WallAPI.java
- ⚠ Risk of bugs, hard to evolve

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Tes$ng DSL
When to build one?

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Test Classifica$on
for taking decisions
§Reliability
- Reproducible: a failure always means a bug
- Flaky eg. tesCng async code, sleep(2) in tests, Selenium
§Speed
- Fast, in process: eg >100 tests/sec è run on CI at each commit
- Slow: load test, batch ... è run Nightly?
§Scope
- Unit Test of a thin feature slice (white-box)
§ Solitary ~ for a single class
§ Social ~ for a cluster of classes fulfilling a well defined responsibility ❤
- Integra;on Test of a long flow, requiring wider awareness
§ Gray-box: Can access my private DB
§ Black-box: Only uses API calls
- Journey Test – a sequence of steps in a stateful interacCon: eg create>search>get>delete

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Contract Mismatch
1) Prevent breaking my contract by accident
- Trick: OpenApiFreezeTest.java
2) Did they change their contract?
= Contract TesAng can automa@cally fail a build if it happens
1) Spring Cloud Contract
2) Pact.io (google "pact victorrentea" for more on that J)

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Start off by writing API-level tests.
Fall back to Unit Tests
when facing too much complexity.

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Convert Unit to Integration Tests
to cover for more risks.
Do it in baby steps,
measuring the added complexity
(intrinsic and extrinsic).

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Cover More Risks
ØLonger flows: confidence and robustness
Ø+DB: queries, JPA magic, TransacCons
Ø+WireMock: correct API integraCon
Ø+Queues: config, ack, retries
ØMagic: @Cacheable, @Retry...
ØEnter via REST: ValidaCon, authz, HTTP status ...
ØStart your app in a Docker: config, 99% real, load

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Take-aways 🍔
🔗 Test IsolaAon: clean up aCer or test-data slices
💥 Flaky Tests: block or poll; test async part separately
🐢 Slow Tests: reuse expensive resources
🧠 CogniAve Load: build a tes@ng DSL (framework)

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Thank you!
victorrentea@gmail.com VictorRentea.ro @victorrentea