Do you recall those buzz words like TDD, BDD? Yep, but we know their problems as well! TDD is too granular. BDD is too coarse-grained. Unit tests are too chatty. BDD is too abstract. TDD requires knowledge of implementation details. BDD does not care about implementation at all. What is in the middle? Integration tests. Let's be Integration driven then! OK, then how to build infrastructure to run Integration tests? Should we start with IaaS first? How to speed up the development and take into account non-foundational requirements like scaling, security borders, isolation, etc. from the very beginning? To answer the questions, we would combine Integration test-based development with serverless (AWS) to solve a typical business task. Based on the example, we would show how to create a solid foundation for further refactoring/refining of the overall solution and concreting it with Unit tests. Acceptance tests would be left for home exercise ;)

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KYIV 2019
How serverless makes Integration TDD a reality.
Why we do need it.
Sergey Medvedev
Enterprise Architect
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Theory
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Why do we need testing?
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- Be able to refactor -> can improve code
- To detect bugs early -> can validate solution quickly
- Be confident in code -> do not be afraid of demo
- Be not afraid of code -> be able to refactor

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Typical test
pyramid
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Typical test
pyramid
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Code dissected
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10% of code for 90% of cases
– Happy path
90% of code for 10% cases –
Sad and Bad paths

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Where to start?
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Start with Integration test for Happy path!

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Practice
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Part 2. Practice
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Domain: Block chain
Goal: Be able to find Nonce to complete block
Limitations:
- Too many competitors -> performance
- Unclear final infrastructure -> prototype
Requirements:
- Need highly scalable solution
- Implementation must follow the standard

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OK, we need some basic theory

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Bitcoin theory.
Simplified
Block chain
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More details: https://5minuteblockchain.com/2019/05/10/blockchain/

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Bitcoin theory.
Simplified
Block structure
.NET CONFERENCE #1 IN UKRAINE KYIV 2019
More details: https://5minuteblockchain.com/2019/05/20/blocks-in-bitcoin/

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Bitcoin theory.
Simplified
Block hash and nonce
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More details: https://en.bitcoin.it/wiki/Block_hashing_algorithm
Bitcoin hash: SHA256(SHA256(Block_Header))
where
- Block_Header is concatenation of HEX’ed values of the following fields
Field Purpose
Version Block version number
hashPrevBlock 256-bit hash of the previous block header
hashMerkleRoot 256-bit hash based on all of the transactions in the block
Time As seconds since 1970-01-01T00:00 UTC
Bits Current difficulty
Nonce
32-bit number (starts at 0, is incremented for each hash.
If Nonce overflows - extraNonce portion of the generation
transaction is incremented, which changes the Merkle
root.

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Bitcoin theory.
Simplified
Merkle root
.NET CONFERENCE #1 IN UKRAINE KYIV 2019
More details: https://5minuteblockchain.com/2019/05/20/blocks-in-bitcoin/

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Everything is clear.
Let’s start programming!

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But, let’s imaging the solution first…

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Solution. Vision
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Component diagram

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Solution. Vision
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Activity diagram

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Where to start?
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Start with Integration test for Happy path!

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Step 1: Basic solution
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Step 1: Basic solution
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Outcome:
• Integration test in "unit test like" style
• we know basic interfaces, models, draft project structure
• we can "run" the solution!!!
• we can split work into at least 2 stream:
• protocol research to identify contracts and refine them -
IBitcoinClient
• continue work on architecture and design for mining - IMiner

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Step 2: Infrastructure & Scaling prototype
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Step 2: Infrastructure
& Scaling prototype
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Outcome:
• Established architecture
• Approach on how to address key problem - scalability
• Can run performance tests
• Not afraid to refactor
• Can split work into multiple streams
• Can validate refactored solution

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Next steps…
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Refactoring goals:
• align implementation with standards
• write unit tests to address Sad/Bad paths
• Improving infrastructure
• Etc.

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Key takeaways
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Serverless
• Quick infrastructure prototyping
• Infrastructure as a Code (IaaC)
Integration test:
• Focus on end result
• Solution scaffolding
• Quick solution to run
• Early demo to engage business
• Framework to develop in parallel by multiple teams with confidence
• Write unit tests for stable parts

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Instead of conclusion…

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Don’t know how to proceed – write tests!
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Thanks and have a green tests!