40 RxJava interview questions (and answers)

RxJava has been gaining popularity in the past couple of years and today is widely adopted in the Android community. So much in fact that I can’t recall an Android developer interview in the past 3 years that doesn’t mention RxJava.

Here is a short list of the most common interview questions I have asked candidates (or been asked as an interviewee). Answers to all questions can be found further down.
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How to setup Jacoco for Android project with Java, Kotlin and multiple flavours

Jacoco is a widely used library to measure test code-coverage in JVM-based projects. Setting it up for Android applications has a few quirks and having multiple flavours, using Kotlin and writing (some) tests in Robolectric makes it even tricker. There are already great tutorials in how to set it up, like THIS and THIS one. In this post however I’ll not only give you a ready solution, but share all details how I got to it – this way you’ll be able to adapt it in the best way for your project.
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Exploring the Android build process: Caching

One of my last tasks @ASOS was to investigate the slow build speeds of the Android application. This post is part of a short series about how we approached the problem, what we tried and what we found out. To be clear, don’t expect miracles and 🦄 here, but you’ll get a better understanding of what you can do to optimise your builds.
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Use custom Hamcrest Matchers to level-up your tests

Ideally automated tests should be predictable, isolated and precise, allowing you to find an issue quickly. If these conditions are met, you’ll never have to change a test unless to accommodate a changed requirement. This sounds great on paper, but in practice we often forget the isolated bit and start testing multiple things in a single test. If abused, we’ll end up with tests that need updating all the time, causing developer frustration and wasting time.

One tool that can help with isolation of tests is using matchers. As the name suggests, matchers allow you to match an object agains certain conditions.
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