LESSON 1 / 8 · Module 1 · Testing Basics

1. The Test Pyramid

[THEORY]

[COMPREHENSION CHECK]

1. Your shop gives 10 % off from ten pieces. After a rule change you want to check the quantities 9, 10 and 11. Which is the cheapest level that answers this?

One integration test with a real database that holds three orders Three end-to-end tests that put 9, 10 and 11 keyboards into the cart in a browser A manual check in the staging environment before every release Three unit tests that call the discount function with 9, 10 and 11

2. OrderRepository.save builds its SQL by hand. Which test can show that the SQL really works?

No dedicated test, because the compiler already checks SQL strings for syntax errors A unit test that checks the generated SQL string with contains("INSERT") A unit test that calls save on an in-memory fake repository and reads the order back An integration test that saves an order into a real database and reads it back

3. A team has 20 unit tests and 400 browser tests. A build takes two hours, and last week a renamed button broke 60 tests. Which change helps most?

Rewrite all browser tests as integration tests that each start a real database Run the browser tests on more machines in parallel to bring the build time down Delete the browser tests and let testers check the shop by hand before every release Put the business rules into unit tests and keep a few browser tests for main flows

4. An end-to-end test fails: the checkout total is wrong for orders with ten items. What should you do first?

Reproduce the wrong total in a unit test, watch it fail, then fix the code Fix the checkout code, then re-run the end-to-end test until it passes Add a second end-to-end test with another quantity to narrow the problem down Mark the end-to-end test as flaky and ignore it until the next release

5. A colleague says: "The pyramid says unit tests matter most, so we do not need any end-to-end tests." What is missing from that argument?

The pyramid asks for as many end-to-end tests as unit tests, just fewer integration tests Wiring only shows in the running system, so a few end-to-end tests are still needed End-to-end tests are the only level that can find bugs in the business rules Nothing is missing, because unit tests already cover everything the other levels cover

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