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Test Smells

Test Smells

Test Smells Test Smells

This repository is designed to serve as a sandbox for exploring a handful of test smells that are common in real-world test suites.

Getting started

First, clone the repo, change into its directory, and make sure your Node.js environment is working okay:

$ npm install $ npm test 

The tests should pass. (If a few tests fail, that’s okay. Some of the tests are designed to fail erratically.)

Working through the repo

Each of our odorous tests are organized under the smells/ directory and broken down into categories.

The tests

Each smell’s file listing is structured the same way, starting with:

The description

Each file starts with a comment which contains:

  • A simple description of the smell
  • An enumeration of the problems the smell might indicate
  • For each potential problem, a general prescribed approach for refactoring the test (or the test’s subject) to eliminate the smell
  • Optionally, a URL pointing to a real-world example of the smell

Remember, not every smell you detect in the wild indicates an actual problem! Smells are simply surface indications of common problems and not necessarily problematic in-and-of themselves.

The subject under test

After the comment will be one to several functions meant to be the "production" source code. Typically these would be broken out into a separate file, but to keep everything straightforward, each smell is kept to a single file listing.

For the purpose of keeping the examples easy-to-understand, the subject code is typically minimal and trivial, unless greater complexity is called for by the test smell itself.

The smelly test

This repo’s tests are written for ourteenytest module, which means that the value of module.exports is considered to be "the test" by the test runner. If module.exports is set to a function, then that’s the only test in the file listing. If a plain object is assigned to module.exports , however, then each function on the object is considered to be its own test. It may be the case that only one of the tests exported by a file exhibit the smell in the description, or that multiple tests could stand to be reworked.

Working with the tests

Identify the smell

Once you’ve read the description of the test smell, try to sniff it out among the file listing’s tests. Usually, only one will exhibit the smell, but use your own judgment to determine which tests should be reworked.

Improve the test

Once you’ve detected a smell, attempt to identify which root cause provided in the description is causing the smell and attempt to implement its prescription for reworking the test. (In a few cases, a test’s improvements will depend on refactoring the subject code, as well.)

Remember, the tests themselves are untested, so be sure that your new-and-improved test still works! Consider forcing the test to break, verifying that a message indicates the test is still doing its job before you commit your changes. As we like to say, "never trust a test you haven’t seen fail."

Compare with our solution

This repo contains a git branch named solutions which will tidy up the tests to our own liking. If you’re interested in seeing our approach to deodorizing a particular test smell, stash or commit your own changes and git checkout solutions to take a peek. When you’re done, switch back to your branch with git checkout - .

If your solution doesn’t look like ours, don’t lose heart! There’s more than one way to write a good test. So long as you’ve resolved the smell and you feel like your changes communicate the intent well, you’ve probably left things in a better state than where you found them.

Help improve this project

There are several ways you can help us make this repo more useful to other developers trying to improve their tests. Here are some ideas of pull requests we’d really appreciate for this repo:

  1. Additional test smells. I’m sure we didn’t catch them all!
  2. URLs pointing to examples of smells. The examples in this repo are necessarily minimal, and as a result there is a risk that they won’t sufficiently remind people of their real-world tests. Additional examples can help people recognize the smells in their own code
  3. Feedback about your experience. If you attended a workshop that used this repo or if you just took a stab at working through it yourself, pleaseopen an issue to tell us about anything else you felt could be improved

If this repo helped you out and you just want to give us a high-five, please say hi on twitter or by e-mail .

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