GET/
with the Pact
Gotchas of
implementing
Contract Testing
the “right” way

Bernardo Guerreiro
Senior Engineer @ Auth0
Platform Team
London, UK (Remote) 2
Twitter: @bernardobridge
Medium: https://medium.com/@bernardobridge

Workshop Requirements
Do I need to know about Pact
already?
Nope. But it can’t hurt!
Do I need a laptop?
No. But you can follow with one!
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Do I need to know Javascript?
No. But it would help to understand
some of the nuances. All concepts
are transferable.
@bernardobridge

A Commit Story - The
Movie
https://github.com/bernardobridge/cinema-services-app/
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@bernardobridge

Part 1
The Curious Case of the Missing Tests
Uhm...someone “forgot” to write tests
again
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Part 2
Finding Testability
FFS! Testing is hard.
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Key Takeaways
▹ You need testability before you need
Pact
▹ Work with developers to achieve that
▹ Mocking dependencies introduces a time
related risk - you never know what’s still
valid
▹ Integration Testing of Microservices can
get very complicated very fast
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Part 3
The Dark Pact
Contract Testing: a hero without a cape
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Key Takeaways
▹ Pact works very similarly to existing
mocking, but you are able to verify validity
of the contract over time
▹ Your contracts should be as narrow as
what your service actually consumes
▹ You can use Matchers to ensure your
contracts are well suited
▹ Provider state allows you to inject data
you may need to use to be able to replicate
calls when verifying the provider
▹ Having consistent naming conventions is
important to this workflow
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@bernardobridge

Part 4
V for Version
My version is better than your version :P
@bernardobridge

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Key Takeaways
▹ Pact pre-verifies versions for you when it
knows the contract hasn’t changed and it
had already been successfully verified
▹ Your provider version can’t just change
when you release, as that’s too late in the
release cycle
▹ You need your provider version to
dynamically change with new code
commits, so you can use commit sha’s
▹ Application Versions in the Pact world are
about what code is running
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Part 5
The Instagram Principle
Click here to tag your location
@bernardobridge

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@bernardobridge

Key Takeaways
▹ If versions are about what piece of code is
running, tags are about where it is running
▹ Branches are a natural candidate for
where the code is running
▹ You can use consumerVersionTags to
filter your provider verification results
▹ Think about the verification step triggered
by the consumer, and the verification step
from normal CI flow as different entities
▹ Make sure you are tagging the latest
master Pact with a prod tag after
releasing to prod. This lets you guarantee
backwards compatibility
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@bernardobridge

Final Thoughts
(you must be tired by now)
@bernardobridge

Getting Started: a few tips
Run POC’s
Proofs of Concept
help establish
confidence in the
time/resource
investment by
demonstrating
usefulness with
minimal investment.
Involve Tech Leads
and Principals
These people have a
wide reach in the
organization, and can
help enforce/nail
down implementation,
proliferation and
technical decisions.
Involve SRE/DevOps
A lot of the hurdles
you will face will be
about retrofitting this
into a CI/CD pipeline.
Get help from the
experts in this area.
You’ll need it!
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Become a Champion
Be the Champion for
adoption of this tool,
running workshops,
brown bags, POC’s
with teams, etc.
Create
RFC’s/equivalent
RFC (Request for
Comments) are a good
way to centralise
knowledge, clear
doubts, but also to
enforce conventions
everyone can adopt.
Get business buy-in
This is not easy, but if
business/product can
understand the value of
this, resource allocation
and help become much
easier to obtain. Pact
works best if everyone
uses it. It should be a
company goal.
@bernardobridge

Useful Links
PACT.io Docs:
https://docs.pact.io/
Workshop Github Repo:
https://github.com/bernardobridge/cinema-services-app
Pact Foundation Slack Channel:
https://slack.pact.io/
UK Gov Lessons Learnt using Contract Testing:
https://technology.blog.gov.uk/2019/01/29/lessons-learnt-using-contract-testing-in-gov-
uk-pay/
Article I wrote about Authentication in Contract Testing:
https://medium.com/dazn-tech/pact-contract-testing-dealing-with-authentication-on-
the-provider-51fd46fdaa78
Installing your Pact Broker on Heroku (outdated version, delete the Gemfile.lock to install
more recent one):
https://github.com/YOU54F/pact-broker-heroku
Atlassian Swagger/Pact Validator:
https://bitbucket.org/atlassian/swagger-mock-validator/src/master/
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THANKS!
Any questions, please
reach out! I’m happy to
help.
You can find me at:
@bernardobridge
https://medium.com/@bernardobridge
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