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Maintainable Integration Testing in React
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Matija Marohnić
February 22, 2018
Programming
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Maintainable Integration Testing in React
Matija Marohnić
February 22, 2018
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Matija Marohnić @silvenon
Maintainable Integration Testing in React
Integration testing Unit testing End-to-end testing
Unit testing Are isolated parts of this feature working?
Integration testing Is this feature supposed to work?
End-to-end testing Does this feature actually work in a real
browser?
$$$ ¢ E2E Integration Unit Testing pyramid
•flaky/brittle •“too much of a hassle” •some features are hard
to test Case against frontend testing
•flaky → pass and fail with the same code •brittle
→ easily broken Flaky/brittle
•an afterthought, something to “deal with later” •not considered an
essential part of development “Too much of a hassle”
•e.g. some advanced APIs •async doesn’t help, it’s often about
timing •developers skip challenging tests, but never return Some features are hard to test
None
•integration tests focus on features •unit tests focus on implementation
details Why “mostly integration”?
How do you feel after writing a test?
None
–Me “A test is useless if you’re equally likely to
make a mistake in the implementation and the test itself.”
•usually developers strive towards 100% •important in libraries and APIs
•not really in frontend application code Test coverage
“You should write tests”
Testing in React
•simulating events •traversing through the tree •mounting in the DOM
or shallow rendering React test utilities
Mounting
Shallow rendering
Shallow vs. mount Unit vs. integration
•a complete testing framework •built-in jsdom •powerful assertions •easy mocking
Jest
•Enzyme •built on top of React’s test utilities •useful high-level
API •Nock •imitates a server Companion tools
Example: DataGrid
None
•opening a DataGrid displays features of the currently selected layer
Testing features Do Don’t •opening a DataGrid makes a certain API request
None
•creating a filter causes features to reduce to an expected
set Testing features Do Don’t •creating a filter displays a chip component
What about the API?
Nock
Nock
•battle-testing some modules in a cheap way •a disposable crutch
during development So when to unit test?
None
If the whole thing works together, chances are that its
parts are working as well