Agenda ● Unit testing introduction ● Differences with other types of tests ● Key concepts ● Rules - things to remember ● A developer’s toolset ● Live coding - hmm… unit testing actually @ppapapetrou76 / @skj_jug Thessaloniki Java Meetup - Unit Testing #skg_unittesting
Unit testing? Why bother? “Code without tests is bad code. It doesn’t matter how well written it is; it doesn’t matter how pretty or object-oriented or well-encapsulated it is. With tests, we can change the behavior of our code quickly and verifiably. Without them, we really don’t know if our code is getting better or worse.” — Michael Feathers Working Effectively With Legacy Code (2004) @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing
Unit testing? Why bother? “Code without unit tests is like American breakfast without eggs & bacon. ” — Patroklos Papapetrou (2014) @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing
What is unit testing? A practice of testing certain functions and areas – or units – of our code. @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing
Advantages ● Identify failures in our algorithms and/or logic ● Approaching development from a unit testing perspective is that you'll likely be writing code that is easy to test ● Prevent future changes from breaking functionality ( safety pillow ) @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing
Assertions? What is that? @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing ● Assertion -> A way to validate expected output / behavior of a method ● Examples ○ Assert.assertEquals (a, b) ○ Assert.assertTrue ( bool ) ● Each unit test should include only one assertion
Mocks / Stubs / Fakes @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing Simulated objects that mimic the behavior of real objects in controlled ways.
Best Practices - Readability @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing ● Setup and teardown methods are not abused. It’s better to use factory methods for readability ● Each test tests one thing only ● Check for good and consistent naming conventions ● Make sure that only meaningful assert messages are used, or none at all (meaningful test names are better)
Best Practices - Readability @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing ● Asserts are separated from actions (different lines). ● Tests don’t use magic strings and values as inputs. use the simplest inputs possible to prove your point. ● There is consistency in location of tests. make it easy to find related tests for a method, or a class, or a project.
Best Practices - Maintainability @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing ● Unit tests are isolated from each other and repeatable ● Testing private or protected methods is not the norm (public is always better) ● Tests are not over-specified ● State-based testing is preferred over using interaction testing
Best Practices - Maintainability @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing ● Strict mocks are used as little as possible (leads to over specification and fragile tests) ● There is no more than one mock per test ● Tests do not mix mocks and regular asserts in the same test (testing multiple things)
Best Practices - Maintainability @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing ● Unit Tests ‘verify’ mock calls only on the single mock object in the test, and not on all the fake objects in the tests ● Unit Tests verify only on a single call to a mock object. Verifying multiple calls on a mock object is either over specification or testing multiple things.
Best Practices - Trust @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing ● Tests does not contain logic or dynamic values ● Check coverage by playing with values (booleans or constants) ● Unit tests are separated from integration tests ● Unit tests don’t use things that keep changing in a unit test (like DateTime.Now ). Use fixed values.
Best Practices - Trust @ppapapetrou76 / @skj_jug #skg_unittesting Thessaloniki Java Meetup - Unit Testing ● Unit tests don’t assert with expected values that are created dynamically - you might be repeating production code. ● Unit tests should not do exception handling.
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