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What is this?

This is a study for deriving a new type of code challenge from a normalised workflow for "tasking a sample react app with modern tools", that actually covers the E2E / full stack process for fetching, displaying, testing and composing a product. This helps to better estimate sprint loads and/or interview full stack engineers in a qualitative way.


Time-Lapse of my creation process is recorded from first commit to completion for dissection; annotated according to gitmoji. I will upload the video at some time.

Stack Challange

  • React 16.7 (incl. Hooks & Suspense)
  • Apollo / GraphQL (using apollo-link-rest)
  • Endpoint with a n+1 aggregation challange (in this case,
  • Sketch App (mocking and interfacing with design; creation of a design system)
  • Styled-Components for implementing a responsive design system

Testing / Quality Assurance

  • Cypress with Mocha & Chai (E2E incl. Unit-Testing)
  • Storybook (component composition strategy & design system validation)

Coinglaze - Code Challange

How to run

  • yarn install
  • yarn start then,for BDD testing
  • yarn cypress:open


  • Create a single page application
  • Using the React Framework
  • Fetch and Display 24h product data from
    • GET /products to get a list of coinbase pairs
    • GET /{id}/stats to get the 24 hours stats of a specific product
  • Illustrate Testing Strategies
    • Assumption: T/BDD
    • Acceptance tests as E2E
    • Basic unit/component tests
  • Should be responsive (mobile / web)

User Storys

  • Epic: As a user, I want to be able to open coinglaze in a web browser.
    • As a user, I can open the website in a modern web browser.
    • As a user, visiting the website with a modern web browser in HD (1080p) resultion displays the website correctly.
    • As a user, visiting the website on a modern smartphone (340p) displays the website correctly.
  • Epic: As a user, I want to be able to see a list of crypto currencies with their 24h stats in my base currency
    • As a user, I can choose my base currency.
    • As a user, I can see a list of crypto currencies.
    • As a user, I can select a crypto currency.
    • As a user, I see the 24h stats of the crypto currency in my base currency, when selected.


  • The task involves a typical n+1 query problem. First the product list, then the product stats need to be fetched; leading to request overhead of n(n-1) with potential for optimisation for base-target currency pairs.
  • The display of results should be responsive
Analysis (Complication)
  • To mitigate the issue of concurrent requests, batching (resolving all possibilities in "one" fetch) is a typical solution to reduce overhead. The other is a tired / just in time fetching approach with a caching solution derived from expected user behaviour.
  • From a user perspective, it is unlikely that I will have interest in the relationship of all n*n relationships of currency pairs, since a user is with highest probability focused one or two pairs. I.e. EUR and USD.
  • Therefore, I will chose a tired solution in which the users base currency is the first layer (or a default, such as EUR) and the pair resolution a product of that.
  • Also, regarding responsiveness, flexbox or css grids are not available in older browsers. Therefore...
Architecture (Solution)
  • ... I make the assumption of targeting evergreen browsers, which is in general the proper approach for start-ups and go to market strategies.
  • As per task, I will use create-react-app for instantiating a new project
  • I will use test runner to formulate (TDD)
    • acceptance/integration tests
    • select user currency of available coinbase base currency
    • show list list of pairs with
    • all info available from /stats
    • unit tests
    • component display etc.
  • As an architect, I want to have a proper caching solution and will therefore rely on apollo-link-rest to perform incremental cacheing and joining of the data to minimize bandwidth; while profiting of extensive unit tests.
  • I will go for a flexbox based design via a tree-shakable UI library and will be using styled-system for granular responsive controls
  • This architecture assumes
    • No infinite product or stats list (aka, no pagination)
    • No server side render (no re-hydration)
    • No progressive web-features (no service workers)
  • Production implementations would use an apollo/prisma/ralay or similar server to join multiple endpoints and proxy only absolutely necessary data for web and mobile clients. Also avoiding unnecessary load on coinbase


Sample Code Challange — Coming up with a code challange that encourages the use of graphql/apollo for a n+1 solution.





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